In a guantlet game the other day I was eliminating players, and every time I did it would not let me continue attacking because I had unplaced bonus units.  However, the place units phase button was grayed out, so the only way I could continue was to leave and re-launch the game.  I'm guessin the same issue could occur with card capture.

So after you relaunched you were able to place units?

Correct

Thanks I'm going to fix these little Player bugs in the next release.