Sorry for digging out this ancient threat, but I have the exact same problem. Any solution by now?

I can prevent expansion of the second toolbar by calling
Qt Code: 
  1. secondToolbar->layout()->setSizeConstraint(QLayout::SetFixedSize);
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but the same approach won't help expand the first toolbar with either constraint. Plus, this will fix both width and height, which is not really what you want.

Thanks for your consideration.