It's probably some left over code that shouldn't quite be there
. It used to be that you could collect the bounty you ourself put, but as far as I've been able to observe that was sealthily changed so you can't collect your own spending - I would guess mostly because there are a few techs that modify the amount spent/gained (Vasari and Advent), so being able to collect what you spend could be exploited as "free cash"
But the AI may not realize that it can't collect what it put up. Unless it's 1v1, though, it still does something