diff --git a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
index 938c1ee7a42d..e8e17b3c6ed2 100644
--- a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
+++ b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
@@ -100,6 +100,13 @@ public class MergeRequestImpl extends MergeRequest {
     myDiffContents[0] = left;
     myDiffContents[1] = base;
     myDiffContents[2] = right;
+
+    if (MergeTool.LOG.isDebugEnabled()) {
+      VirtualFile file = base.getFile();
+      MergeTool.LOG.debug(new Throwable(base.getClass() + " - writable: " + base.getDocument().isWritable() + ", contentType: " +
+                                        base.getContentType() + ", file: " + (file != null ? "valid - " + file.isValid() : "null") +
+                                        ", presentation: " + myOkButtonPresentation + "-" + myCancelButtonPresentation));
+    }
   }
 
   @Override
diff --git a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeTool.java b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeTool.java
index f8a025a3d2d7..489361e9067d 100644
--- a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeTool.java
+++ b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeTool.java
@@ -16,6 +16,7 @@
 package com.intellij.openapi.diff.impl.mergeTool;
 
 import com.intellij.openapi.Disposable;
+import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.diff.DiffContent;
 import com.intellij.openapi.diff.DiffRequest;
 import com.intellij.openapi.diff.DiffTool;
@@ -29,11 +30,16 @@ import org.jetbrains.annotations.NotNull;
 import java.awt.*;
 
 public class MergeTool implements DiffTool {
+  public static final Logger LOG = Logger.getInstance(MergeTool.class);
+
   public void show(DiffRequest data) {
     if (data instanceof MergeRequestImpl) {
       showDialog((MergeRequestImpl)data);
       return;
     }
+    if (LOG.isDebugEnabled()) {
+      LOG.debug(new Throwable("MergeTool - frame"));
+    }
     FrameWrapper frameWrapper = new FrameWrapper(data.getProject(), data.getGroupKey());
     DiffViewer mergePanel = createMergeComponent(data, null, frameWrapper);
     frameWrapper.setComponent(mergePanel.getComponent());
@@ -51,6 +57,9 @@ public class MergeTool implements DiffTool {
   }
 
   private static void showDialog(MergeRequestImpl data) {
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("MergeTool - dialog");
+    }
     DialogBuilder builder = new DialogBuilder(data.getProject());
     builder.setDimensionServiceKey(data.getGroupKey());
     builder.setTitle(data.getWindowTitle());
@@ -82,6 +91,9 @@ public class MergeTool implements DiffTool {
 
   @Override
   public DiffViewer createComponent(String title, DiffRequest request, Window window, @NotNull Disposable parentDisposable) {
+    if (LOG.isDebugEnabled()) {
+      LOG.debug(new Throwable("MergeTool - component: " + request.getContents()[1].getDocument().isWritable()));
+    }
     return createMergeComponent(request, null, parentDisposable);
   }
 }
diff --git a/platform/vcs-impl/src/com/intellij/openapi/vcs/changes/patch/ApplyPatchAction.java b/platform/vcs-impl/src/com/intellij/openapi/vcs/changes/patch/ApplyPatchAction.java
index b11fea49e374..d86b54d7c5c1 100644
--- a/platform/vcs-impl/src/com/intellij/openapi/vcs/changes/patch/ApplyPatchAction.java
+++ b/platform/vcs-impl/src/com/intellij/openapi/vcs/changes/patch/ApplyPatchAction.java
@@ -29,6 +29,8 @@ import com.intellij.openapi.application.Application;
 import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.diff.*;
+import com.intellij.openapi.diff.impl.external.DiffManagerImpl;
+import com.intellij.openapi.diff.impl.mergeTool.MergeTool;
 import com.intellij.openapi.diff.impl.patch.*;
 import com.intellij.openapi.diff.impl.patch.apply.ApplyFilePatch;
 import com.intellij.openapi.diff.impl.patch.apply.ApplyFilePatchBase;
@@ -286,8 +288,21 @@ public class ApplyPatchAction extends DumbAwareAction {
     if (fileContent == null || content == null) {
       return ApplyPatchStatus.FAILURE;
     }
+
+    if (MergeTool.LOG.isDebugEnabled()) {
+      MergeTool.LOG.debug("ApplyPatch: project: " + project + ", document: " + document + ", file.valid: " + file.isValid() +
+                          ", fileType: " + file.getFileType() + (document != null ? ", writable: " + document.isWritable() : ""));
+    }
+
     final MergeRequest request = mergeRequestFactory.createMergeRequest(fileContent.toString(), patchedContent, content.toString(), file,
                                                                         project, reverse, leftPanelTitle, rightPanelTitle);
+
+    if (MergeTool.LOG.isDebugEnabled()) {
+      DiffContent baseContent = request.getContents()[1];
+      MergeTool.LOG.debug("ApplyPatch: base content: " + baseContent.getClass() + ", writable: " + baseContent.getDocument().isWritable());
+      MergeTool.LOG.debug("Custom DiffTools: " + DiffManagerImpl.getInstanceEx().getAdditionTools());
+    }
+
     DiffManager.getInstance().getDiffTool().show(request);
     if (request.getResult() == DialogWrapper.OK_EXIT_CODE) {
       return ApplyPatchStatus.SUCCESS;