Created attachment 106718 [details] Capture showing messed up buttons If I run multiple instances of KCalc I frequently see many of the buttons getting messed up as is shown in the picture I have attached. I have seen this problem for quite some time. Note that I typically use Numeral Systems Mode with show bit edit selected, though the bit edit mode doesn't seem to affect this. When this problem shows up it shows up in all modes except simple mode.
Created attachment 106719 [details] Image showing both instances Added second image
Looks like your Ctrl key is pressed.
As Christoph said, this behavior is likely caused by pressing "Ctrl". If this behavior happens without you pressing the "Ctrl" key, please reopen the bug report.