You need to use the 'Button: On clicked' trigger with buttons. Not the Mouse click trigger.
Also when you have something like this:
[quote:1lpgw5rp]
The first condition will pick the button you clicked. In the sub-event you have only that button picked, so the 'pick by UID' will only pick that same button if the UIDs match, otherwise it can't pick anything. And again in the next sub-event, there can only be one button picked at this point so no need for a loop.
If you have something picked already and you want to pick another instance in a sub-event then you need a 'System: Pick all' condition first.