diff -Naur qt-x11-opensource-src-4.5.0-beta1-orig/src/gui/kernel/qapplication_x11.cpp qt-x11-opensource-src-4.5.0-beta1/src/gui/kernel/qapplication_x11.cpp
--- qt-x11-opensource-src-4.5.0-beta1-orig/src/gui/kernel/qapplication_x11.cpp	2008-12-17 20:16:41.000000000 +0300
+++ qt-x11-opensource-src-4.5.0-beta1/src/gui/kernel/qapplication_x11.cpp	2009-01-03 18:00:28.000000000 +0300
@@ -4252,6 +4252,10 @@
             }
 #endif
             type = QEvent::MouseButtonRelease;
+	    // HACK: if recieved ButtonRelease event qt_button_down - can't be NULL, because
+	    // no ButtonRelease without ButtonPress event
+            if (!qt_button_down)
+                qt_button_down = this;
         }
     }
     mouseActWindow = effectiveWinId();                        // save some event params