This is not what a bug is. It's a result of design choices, and we know about it.
Just wandering if the devs thinks its working as intended. If yes then its ok with me. if not just use the fix below.
Thanks for your respond Noon sir.
Possible fix :
From KyleAkira :
I think the solution could be easy by just don't letting capture vehicles when your pop is over 100.
i.e:
99 pop and you recrew a tank: YES you can (pop is now 109)
101 pop and you try to recrew a tank: NO you can't get inside any tank until you low your pop less than 100, you can decrew other tanks to just crew new ones.
Just disable de order of recrewing tanks when clicking on it if your pop cap is on the limit.