How to reproduce:
1) make a rectangular selection (Alt+Shift+cursor)
2) start a search (Ctrl+F) => selection turns to a black-border rectangle
3) activate regexp search (in the context menu of the rightmost icon in the search textline)
4) type the circumflex character "^" with no line start or "$" with no line end in the selection

Effect:
QtCreator seems to lock up. No more keyboard or mouse input is accepted. Still, the refreshes of the widgets seem to be made correctly (no "ghosts"/unrefreshed rectangles in QtCreator window upon move or hide/show etc.)

Expected:
QtCreator should not lock.

Additional info:
typing anything else than the circumflex or the dollar sign character at step 4) (i.e. normal letters or even punctuation) doesn't produce the lock.