I'm developing GUI application on a team with Qt Creator 2.6.1 and encountered a strange problem.
In design mode of Qt Creator, I can't add/move widgets in some *.ui files which my coworker created, by mouse's drug & drop operation.
I can move those by cursor keys (up, down, left, right key on keyboard) or setting the geometry x&y manually.
But by drug and drop, I can't add/move widgets.

ui files I created are OK.
Some ui files he created are OK.
But other files he created, I can't add/move widgets by drug and drop.
(somehow I can do with Qt Designer)

We are using same version of Qt Creator ver 2.6.1 and configurations are same.
It seems my Qt designer have something problem.
Re-installing Qt creator couldn't solve it.

Can anyone help?