TWAIN DLL that spawns a thread that creates a GUI works on Qt 4.8 died on Qt 5.1.1

I’m trying to understand how Qt 4.8 changed – maybe in terms of threading.

I created a DLL for a TWAIN compliant app. This DLL is controlled by an application which is the main thread (it is not a Qt application) . This DLL then spawns a thread and in that thread creates and displays a GUI.

This model structure seemed to work without issue in Qt 4.8.4. Having migrated to Qt 5.1.1 the DLL builds and runs but there are no QDialog messages that are being processed – the GUI has no controls working - seems dead, just displays.

First question is: Is this model/structure possible in Qt 5? Was there changes that would affect this from working as it did in Qt 4.8?

Second question: Is there a preferred way of doing this? This structure is for creating a TWAIN data source. Anyone having any mileage with writing TWAIN compliant apps please chime in.

Thanks in advance