BleachBit invalidates shared memory included our shared data cashes. Any KDE application using will crash once the memory got invalidated. As to my knowledge Oxygen is a heavy user of the shared data cache any GUI application is affected.
If you think that you need to use BleachBit I recommend to read the wonderful article on lwn about it: BleachBit: Does GNU/Linux need the equivalent of a Windows registry cleaner? If you don’t know what it is, just forget about it, but warn anyone who you will see using it.