REG: No slots visible in Signal/Slot Editor slot combo-box delegate

To reproduce:

• start designer,
• choose "new dialog with buttons right"
• in Signal/Slot Editor you can see two connections: between buttonBox's accepted() and Dialog's accept(), and buttonBox's rejected() and Dialog's reject();
• when you double-click on slot "reject()" (the last column) a combo box is correctly opened, but ... it's empty: the only item there is "<slot>".

This used to work fine. The only change is that we applied dd7873cd7e02e42b384709f33a34f69bc06fb25d (patch from the partent task), so this "fix" for QTBUG-17179 must have introduced the problem?