infinite loop in Rebuild Watchmodel process

I have infinite loop when debugging any program that contains QModelIndex object
Effect is that Rebuild Watchmodel is infinitly repeated.

How to reproduce:

Take Qt example: addressbook in qtbase/examples/widgets/itemviews/addressbook

Add break point in addressbookwidget.cpp:L85

Run with debugger log open.

Run to breakpoint (add an entry).
In debugger extend the following variable:

• index (Goes fine)
• then extend sub-field m
  The log shows that we have entered into an infinite loop rebuilding the watchmodel.

I am using git master with today fetch/update.