First of all look up into ur code if you are any how capturing Delete key. Check if you have used :

setShortcut(tr("Delete"));

any where in your code.

As this will capture Delete key on application level prevent the KeyPressEvent to capture Qt::Key_Delete. I have also faced the similar problem. The moment i commented this piece of line KeyPressEvent captured the Qt::Key_Delete. Thiswas the only possible way we were not able to capture key Qt::Key_Delete with keypressevent.