diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 09f8bfa3a..29227606d 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.geometerplus.zlibrary.ui.android" android:versionCode="10105" android:versionName="1.1.5" android:installLocation="auto">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.geometerplus.zlibrary.ui.android" android:versionCode="10106" android:versionName="1.1.6" android:installLocation="auto">
 	<uses-sdk android:minSdkVersion="4" android:maxSdkVersion="10"/>
 	<supports-screens android:smallScreens="true" android:normalScreens="true" android:largeScreens="true" android:anyDensity="true" />
 	<uses-permission android:name="android.permission.INTERNET" />
diff --git a/VERSION b/VERSION
index e25d8d9f3..0664a8fd2 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.1.5
+1.1.6
diff --git a/src/org/geometerplus/android/fbreader/library/LibraryActivity.java b/src/org/geometerplus/android/fbreader/library/LibraryActivity.java
index 80399f630..7e86b40ad 100644
--- a/src/org/geometerplus/android/fbreader/library/LibraryActivity.java
+++ b/src/org/geometerplus/android/fbreader/library/LibraryActivity.java
@@ -127,7 +127,7 @@ public class LibraryActivity extends BaseActivity implements MenuItem.OnMenuItem
 
 	@Override
 	protected void onActivityResult(int requestCode, int returnCode, Intent intent) {
-		if (requestCode == BOOK_INFO_REQUEST) {
+		if (requestCode == BOOK_INFO_REQUEST && intent != null) {
 			final String path = intent.getStringExtra(BookInfoActivity.CURRENT_BOOK_PATH_KEY);
 			final Book book = Book.getByFile(ZLFile.createFileByPath(path));
 			myLibrary.refreshBookInfo(book);
diff --git a/src/org/geometerplus/android/fbreader/library/SQLiteBooksDatabase.java b/src/org/geometerplus/android/fbreader/library/SQLiteBooksDatabase.java
index fd6107fad..cbb7392bf 100644
--- a/src/org/geometerplus/android/fbreader/library/SQLiteBooksDatabase.java
+++ b/src/org/geometerplus/android/fbreader/library/SQLiteBooksDatabase.java
@@ -50,12 +50,13 @@ public final class SQLiteBooksDatabase extends BooksDatabase {
 	}
 
 	protected void executeAsATransaction(Runnable actions) {
-		myDatabase.beginTransactionNonExclusive();
+		myDatabase.execSQL("BEGIN IMMEDIATE");
 		try {
 			actions.run();
-			myDatabase.setTransactionSuccessful();
+		} catch (Throwable t) {
+			myDatabase.execSQL("ROLLBACK");
 		} finally {
-			myDatabase.endTransaction();
+			myDatabase.execSQL("END");
 		}
 	}
 
diff --git a/src/org/geometerplus/zlibrary/core/tree/ZLTree.java b/src/org/geometerplus/zlibrary/core/tree/ZLTree.java
index b3036fe12..677c4356f 100644
--- a/src/org/geometerplus/zlibrary/core/tree/ZLTree.java
+++ b/src/org/geometerplus/zlibrary/core/tree/ZLTree.java
@@ -25,19 +25,19 @@ public abstract class ZLTree<T extends ZLTree<T>> implements Iterable<T> {
 	private int mySize = 1;
 	public final T Parent;
 	public final int Level;
-	private ArrayList<T> mySubTrees;
+	private volatile List<T> mySubTrees;
 
 	protected ZLTree() {
 		this(null);
 	}
 
 	protected ZLTree(T parent) {
-		this(parent, (parent == null) ? 0 : parent.subTrees().size());
+		this(parent, (parent == null) ? 0 : parent.mySubTrees.size());
 	}
 
 	protected ZLTree(T parent, int position) {
-		if (parent != null && (position < 0 || position > parent.subTrees().size())) {
-			throw new IndexOutOfBoundsException("`position` value equals " + position + " but must be in range [0; " + parent.subTrees().size() + "]");
+		if (parent != null && (position < 0 || position > parent.mySubTrees.size())) {
+			throw new IndexOutOfBoundsException("`position` value equals " + position + " but must be in range [0; " + parent.mySubTrees.size() + "]");
 		}
 		Parent = parent;
 		if (parent != null) {
@@ -57,43 +57,51 @@ public abstract class ZLTree<T extends ZLTree<T>> implements Iterable<T> {
 	}
 
 	public final List<T> subTrees() {
-		if (mySubTrees == null) {
-			return Collections.emptyList();
+		synchronized (mySubTrees) {
+			if (mySubTrees == null) {
+				return Collections.emptyList();
+			}
+			return new ArrayList(mySubTrees);
 		}
-		return mySubTrees;
 	}
 
 	public final T getTreeByParagraphNumber(int index) {
-		if ((index < 0) || (index >= mySize)) {
-			// TODO: throw exception?
+		if (index < 0 || index >= mySize) {
+			// TODO: throw an exception?
 			return null;
 		}
 		if (index == 0) {
 			return (T)this;
 		}
 		--index;
-		for (T subtree : mySubTrees) {
-			if (subtree.mySize <= index) {
-				index -= subtree.mySize;
-			} else {
-				return (T)subtree.getTreeByParagraphNumber(index);
+		synchronized (mySubTrees) {
+			for (T subtree : mySubTrees) {
+				if (subtree.mySize <= index) {
+					index -= subtree.mySize;
+				} else {
+					return (T)subtree.getTreeByParagraphNumber(index);
+				}
 			}
 		}
 		throw new RuntimeException("That's impossible!!!");
 	}
 
 	private void addSubTree(T subtree, int position) {
-		if (mySubTrees == null) {
-			mySubTrees = new ArrayList<T>();
+		synchronized (this) {
+			if (mySubTrees == null) {
+				mySubTrees = Collections.synchronizedList(new ArrayList<T>());
+			}
 		}
 		final int subTreeSize = subtree.getSize();
-		final int thisSubTreesSize = mySubTrees.size();
-		while (position < thisSubTreesSize) {
-			subtree = mySubTrees.set(position++, subtree);
-		}
-		mySubTrees.add(subtree);
-		for (ZLTree<?> parent = this; parent != null; parent = parent.Parent) {
-			parent.mySize += subTreeSize;
+		synchronized (mySubTrees) {
+			final int thisSubTreesSize = mySubTrees.size();
+			while (position < thisSubTreesSize) {
+				subtree = mySubTrees.set(position++, subtree);
+			}
+			mySubTrees.add(subtree);
+			for (ZLTree<?> parent = this; parent != null; parent = parent.Parent) {
+				parent.mySize += subTreeSize;
+			}
 		}
 	}
 
@@ -102,8 +110,10 @@ public abstract class ZLTree<T extends ZLTree<T>> implements Iterable<T> {
 		ZLTree<?> parent = Parent;
 		if (parent != null) {
 			parent.mySubTrees.remove(this);
-			if (parent.mySubTrees.isEmpty()) {
-				parent.mySubTrees = null;
+			synchronized (parent) {
+				if (parent.mySubTrees.isEmpty()) {
+					parent.mySubTrees = null;
+				}
 			}
 			for (; parent != null; parent = parent.Parent) {
 				parent.mySize -= subTreeSize;
@@ -113,7 +123,9 @@ public abstract class ZLTree<T extends ZLTree<T>> implements Iterable<T> {
 
 	public final void clear() {
 		final int subTreesSize = mySize - 1;
-		mySubTrees = null;
+		synchronized (this) {
+			mySubTrees = null;
+		}
 		mySize = 1;
 		if (subTreesSize > 0) {
 			for (ZLTree<?> parent = Parent; parent != null; parent = parent.Parent) {
@@ -157,10 +169,12 @@ public abstract class ZLTree<T extends ZLTree<T>> implements Iterable<T> {
 				while (!myIndexStack.isEmpty()) {
 					final int index = myIndexStack.removeLast() + 1;
 					parent = parent.Parent;
-					if (parent.mySubTrees.size() > index) {
-						myCurrentElement = parent.mySubTrees.get(index);
-						myIndexStack.add(index);
-						break;
+					synchronized (parent.mySubTrees) {
+						if (parent.mySubTrees.size() > index) {
+							myCurrentElement = parent.mySubTrees.get(index);
+							myIndexStack.add(index);
+							break;
+						}
 					}
 				}
 				if (myIndexStack.isEmpty()) {