The steps to reproduce (Failing) are:
1. emacs -Q -nw -l /tmp/.emacs-rc-cedet-nil.el -f cedet-lambda/load-qt4 /tmp/cedet/impressive/qt4/main_cedet_demo.cpp 
2. M-g g 10
4. C-e
5. M-x semantic-ia-complete-symbol-menu

It fails and show those messages:
--8<---------------cut here---------------start------------->8---
(error "Cannot find types for ‘QPushButton quit ()’")
No smart completions found.
--8<---------------cut here---------------end--------------->8---

The steps to reproduce (WORKAROUND) are:
1. emacs -Q -nw -l /tmp/.emacs-rc-cedet-t.el -f cedet-lambda/load-qt4 /tmp/cedet/impressive/qt4/main_cedet_demo.cpp -f semantic-mode
2. M-g g 10
4. C-e
5. M-x semantic-ia-complete-symbol-menu

As You could see on the image 'cedet-qt4-demo-t.png'. It works. And on
the image 'cedet-qt4-demo-fails.png' it fails. The difference is the way
the funct 'semantic-mode' is invoked.

Best Regards
Andrés Ramírez