Keyboard shortcuts not working at all or at first

This is driving me nuts: Ever so often Keyboard shortcuts don't work at the first try or don't work at all. For example I can't ungroup stuff at one time - the other time it works. Ungrouping the same object via menu works. This doesn't just happen on my machine - also at work. I must stick with CDRX6 due to work policy - so updating to 7 is not an option. Can anyone shed some light?