"Selecting block up" overselects when a diacritic is present

In the animation below I focus on upper string and press Ctrl+u. The string gets selected properly. Then I focus on lower string and press Ctrl+u. The string gets selected not properly.

Steps to reproduce:

1. unpack the attached template.zip
2. open CMakeLists.txt in QtCreator
3. place the cursor inside "abć" string
4. press Ctrl+u to invoke "Select block up" feature

Behavior:

"abć gets selected (four chars)

Expected behavior:

abć gets selected (three chars)