The explicit "Clean whitespace" feature (either via Edit menu or shortcut) no longer works in Creator 4.13. It definitely still worked in 4.12 versions.
Steps to repeat:
1) Configure "Spaces only" under "Text editor" - "Behavior"
2) Open a Qt example with c++ source code of your choice
3) Open one of the source files in an external text editor
4) Enter several tabs into a blank line
5) Open the same source file in Qt Creator
6) Select the whole source file "Select all and "Clean whitespace" via Edit->Advanced
And Nothing happens