This bug affects the mpx branch and I've verified that it does not occur in the master branch.
Qt-based scrollbars do not respond to any sort of mouse input (except for the scrollwheel). They don't light up when the mouse is over them, and no part responds to clicks or drags. Every Qt app I've tried displayed this problem: Konsole, KWrite, Kate, KDiff3. All other parts of the GUI are functional.
This is on Ubuntu Hardy with libqt3-mt version 3:3.3.8-b-0ubuntu3.
Problem was caused by a wrong state field in the event. The code assembled the
state after updating the device and as a result, the state included the change
initiated by the event. This is against the specs, and caused the Qt
scrollbars to fail. Simply generating the state before updating the device
resolves the problem.
Fixed here, will be fixed in upstream as soon as I can push again. Thanks for
pushed as 28378d26b4bae377ef1212f6a51cda9b5529f1b5.