https://github.com/enthought/traitsui/issues/74
diff -ur traitsui-4.3.0.orig/traitsui/qt4/ui_panel.py traitsui-4.3.0/traitsui/qt4/ui_panel.py
--- traitsui/qt4/ui_panel.py	2013-03-29 04:08:54.000000000 +0800
+++ traitsui/qt4/ui_panel.py	2013-04-12 13:23:09.499989912 +0800
@@ -977,7 +977,7 @@
 
         if (label is not None
             and not is_label_left
-            and item_policy == QtGui.QSizePolicy.Policy.Minimum):
+            and item_policy == QtGui.QSizePolicy.Minimum):
             # this item cannot be stretched horizontally, and the label
             # exists and is on the right -> make label stretchable if necessary
 
@@ -1012,7 +1012,7 @@
         label_policy = label.sizePolicy()
         label_policy.setHorizontalStretch(stretch)
         label_policy.setHorizontalPolicy(
-            QtGui.QSizePolicy.Policy.Expanding)
+            QtGui.QSizePolicy.Expanding)
         label.setSizePolicy(label_policy)
 
 
diff -ur traitsui-4.3.0.orig/traitsui/tests/_tools.py traitsui-4.3.0/traitsui/tests/_tools.py
--- traitsui/tests/_tools.py	2013-03-29 04:08:54.000000000 +0800
+++ traitsui/tests/_tools.py	2013-04-12 13:23:09.502989914 +0800
@@ -173,7 +173,7 @@
         return ui_control.GetSizeTuple()
 
     elif is_current_backend_qt4():
-        return ui_control.size().toTuple()
+        return ui_control.size().width(), ui_control.size().height()
 
 
 # ######### Debug tools