diff --git a/python/ipnb/src/org/jetbrains/plugins/ipnb/editor/panels/IpnbFilePanel.java b/python/ipnb/src/org/jetbrains/plugins/ipnb/editor/panels/IpnbFilePanel.java
index 82fe0cd0dfec..47915f6d5f09 100644
--- a/python/ipnb/src/org/jetbrains/plugins/ipnb/editor/panels/IpnbFilePanel.java
+++ b/python/ipnb/src/org/jetbrains/plugins/ipnb/editor/panels/IpnbFilePanel.java
@@ -105,6 +105,7 @@ public class IpnbFilePanel extends JPanel implements Scrollable, DataProvider, D
     try {
       IpnbFile file = IpnbParser.parseIpnbFile(myDocument, myVirtualFile);
       if (file.equals(myIpnbFile)) return;
+      removeAll();
       myIpnbFile = file;
       myIpnbPanels.clear();
       mySelectedCell = null;
@@ -348,7 +349,6 @@ public class IpnbFilePanel extends JPanel implements Scrollable, DataProvider, D
       final IpnbEditablePanel selectedCell = getSelectedCell();
       final int index = myIpnbPanels.indexOf(selectedCell);
       myInitialSelection = index >= 0 && index < myIpnbPanels.size() ? index : myIpnbPanels.size() - 1;
-      removeAll();
       readFromFile(false);
     }
   }
diff --git a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/IpnbFile.java b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/IpnbFile.java
index 856319716fb0..2e743b23f3bf 100644
--- a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/IpnbFile.java
+++ b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/IpnbFile.java
@@ -10,9 +10,9 @@ public class IpnbFile {
   private final Map<String, Object> myMetadata;
   private final int myNbformat;
   private final List<IpnbCell> myCells;
-  private final String myPath;
+  @NotNull private final String myPath;
 
-  public IpnbFile(Map<String, Object> metadata, int nbformat, List<IpnbCell> cells, String path) {
+  public IpnbFile(Map<String, Object> metadata, int nbformat, List<IpnbCell> cells, @NotNull String path) {
     myMetadata = metadata;
     myNbformat = nbformat;
     myCells = cells;
@@ -31,6 +31,7 @@ public class IpnbFile {
     myCells.remove(index);
   }
 
+  @NotNull
   public String getPath() {
     return myPath;
   }
@@ -43,4 +44,27 @@ public class IpnbFile {
     return myNbformat;
   }
 
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+
+    IpnbFile file = (IpnbFile)o;
+
+    if (myNbformat != file.myNbformat) return false;
+    if (myMetadata != null ? !myMetadata.equals(file.myMetadata) : file.myMetadata != null) return false;
+    if (myCells != null ? !myCells.equals(file.myCells) : file.myCells != null) return false;
+    if (!myPath.equals(file.myPath)) return false;
+
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    int result = myMetadata != null ? myMetadata.hashCode() : 0;
+    result = 31 * result + myNbformat;
+    result = 31 * result + (myCells != null ? myCells.hashCode() : 0);
+    result = 31 * result + (myPath.hashCode());
+    return result;
+  }
 }
\ No newline at end of file
diff --git a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/IpnbEditableCell.java b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/IpnbEditableCell.java
index cf62f52810b3..52914fa2c61c 100644
--- a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/IpnbEditableCell.java
+++ b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/IpnbEditableCell.java
@@ -34,4 +34,24 @@ public abstract class IpnbEditableCell implements IpnbCell {
   public Map<String, Object> getMetadata() {
     return myMetadata;
   }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+
+    IpnbEditableCell cell = (IpnbEditableCell)o;
+
+    if (!mySource.equals(cell.mySource)) return false;
+    if (myMetadata != null ? !myMetadata.equals(cell.myMetadata) : cell.myMetadata != null) return false;
+
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    int result = mySource.hashCode();
+    result = 31 * result + (myMetadata != null ? myMetadata.hashCode() : 0);
+    return result;
+  }
 }
diff --git a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/output/IpnbOutputCell.java b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/output/IpnbOutputCell.java
index 487d762c55b0..85d64911a3c9 100644
--- a/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/output/IpnbOutputCell.java
+++ b/python/ipnb/src/org/jetbrains/plugins/ipnb/format/cells/output/IpnbOutputCell.java
@@ -37,4 +37,26 @@ public class IpnbOutputCell implements IpnbCell {
   public Map<String, Object> getMetadata() {
     return myMetadata;
   }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+
+    IpnbOutputCell cell = (IpnbOutputCell)o;
+
+    if (myPromptNumber != null ? !myPromptNumber.equals(cell.myPromptNumber) : cell.myPromptNumber != null) return false;
+    if (myText != null ? !myText.equals(cell.myText) : cell.myText != null) return false;
+    if (myMetadata != null ? !myMetadata.equals(cell.myMetadata) : cell.myMetadata != null) return false;
+
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    int result = myPromptNumber != null ? myPromptNumber.hashCode() : 0;
+    result = 31 * result + (myText != null ? myText.hashCode() : 0);
+    result = 31 * result + (myMetadata != null ? myMetadata.hashCode() : 0);
+    return result;
+  }
 }