REG: Q3MainWIndow contents sizing problems

I have an application (Recoll) which was written for Qt3, and runs under Qt4. The main window is a Q3MainWindow, the ui file is converted from Qt3 by uic3. This has worked from Qt 4.3 to 4.6.0
At some point between 4.6.0 and 4.6.1, the sizing of the main window components ceased to work (this was reported first from an openSuse gui using a snapshot between 4.6.0 and 4.6.1). I have verified the problem with 4.6.1 on Linux and MacOS X

The symptom is that the main window contents do not resize with the window. In addition my window has 2 toolbars, and they are stacked one over the other on the left of the toolbar area.

I am going to try and produce a minimal example which I do not have for now. This report is mainly in case this rings a bell with someone and a suggestion for a workaround can be found.