It is possible to Hang Qt Creator by using the file search functionality with regular expressions.

Steps to reproduce:

1) I opened a file for editing
2) Ctrl+F
3) Switch to search case insensitive and regular expressions
4) search for e.g. a

=> all is fine
5) select 1 and replace by 2 => all is fine, too
6) replace 2 between {} => hangs

It doesn't matter what regexp symbol you are looking for, it seems the {} causes this hang.