Thanks for the tip!
I tried it, but it reported no obvious error.

But I recognized the following:

1. In the simple case (without using QSortFilterProxyModel), I saw this output from the ModelTest:

ratbr QModelIndex(-1,-1,0x0,QObject(0x0) ) 1 0
rr QModelIndex(-1,-1,0x0,QObject(0x0) ) 1 0

2. In the problematic second case (with using QSortFilterProxyModel) these output are missing!

Are the signals are not passed correctly?

Any other ideas?

Regards
Sven