Standard QT drag / drop event code to transfer data between widgets produces a combase error and causes GUI thread to stall. Reproducable in QT examples in both debug and release builds with MINGW and MSVC.

onecore\com\combase\dcomrem\resolver.cxx(2491)\combase.dll!00007FFD1A377992: (caller: 00007FFD1A2C2075) ReturnHr(1) tid(399c) 80040154 Class not registered

Reproducible when a drag event is in progress but it is not catageorized as one of the following:

• dragMoveEvent
• dragEnterEvent
• dragLeaveEvent
• dropEvent

In other words, if an item is dragged and mouse stops on the receiving widget.

Related QT forum post:

https://forum.qt.io/topic/123927/qdrag-qdropevent-combase-error-class-not-registered/14