Hi,
I also tried the mouseRelease function and it did not work, I looked into it a bit more , if you read the QWidget::grabMouse() description it says that mouse events are automatically grabbed in a widget. Without knowing the details of your implementation, here are some other suggestions.
Look in the QWidget Class Reference, you may have two choices.
#1 - disable the widget using QWidget::setEnabled - setting the value to false will disable the widgets - any events to that widget. Not sure if this will have a side effect to your functionality to that widget.
#2 - reimplement the virtual function QWidget::mousePressEvent and just ignore any mouse events from there. This may be safer.
Good luck.