diff --git a/src/cutselectionController.py b/src/cutselectionController.py
index 3671cb4..abf579c 100644
--- a/src/cutselectionController.py
+++ b/src/cutselectionController.py
@@ -572,7 +572,7 @@ def sceneChangeCallback(self,filename,timestamp,timestampEnd=None,kind='Mark'):
     elif kind == 'Cut':
       self.videoManager.registerNewSubclip(filename,timestamp,max(timestamp+0.01,timestampEnd-0.01))
     self.updateProgressStatistics()
-    self.ui.setUiDirtyFlag()
+    self.ui.setUiDirtyFlag(withLock=True)
 
   def askToUseRangeIfSet(self):
     useRange=False
diff --git a/src/cutselectionUi.py b/src/cutselectionUi.py
index 0e78b22..e43e5df 100644
--- a/src/cutselectionUi.py
+++ b/src/cutselectionUi.py
@@ -913,12 +913,12 @@ def getIsPlaybackStarted(self):
         return self.controller.getIsPlaybackStarted()
 
     def update(self,withLock=True):
-        self.frameTimeLineFrame.updateCanvas(withLock=True)
+        self.frameTimeLineFrame.updateCanvas(withLock=False)
 
-    def setUiDirtyFlag(self):
+    def setUiDirtyFlag(self,withLock=False):
       self.frameTimeLineFrame.setUiDirtyFlag()
       try:
-        self.frameTimeLineFrame.updateCanvas() 
+        self.frameTimeLineFrame.updateCanvas(withLock=withLock) 
       except Exception as e:
         print(e)
 
diff --git a/src/timeLineSelectionFrameUI.py b/src/timeLineSelectionFrameUI.py
index 04bc1eb..0a71f58 100644
--- a/src/timeLineSelectionFrameUI.py
+++ b/src/timeLineSelectionFrameUI.py
@@ -14,7 +14,17 @@
 import math
 
 from contextlib import contextmanager
-from contextlib import AbstractContextManager
+
+class AbstractContextManager:
+
+  def __init__(self):
+    pass
+
+  def __enter__(self):
+    pass
+
+  def __exit__(self ,type, value, traceback):
+    pass
 
 
 @contextmanager
@@ -785,7 +795,7 @@ def requestFrames(self,filename,startTime,Endtime,timelineWidth,frameWidth):
     self.framesRequested=self.controller.requestTimelinePreviewFrames(filename,startTime,Endtime,frameWidth,timelineWidth,self.frameResponseCallback)
 
   def updateCanvas(self,withLock=False):
-  
+    
     if withLock:
       updateLock = acquire_timeout(self.uiUpdateLock,0.1)
     else: