After the conclusion of last round's combat he drew the mandatory chit "pantalons rouge" which is supposed to be played only by the french.
Since it's a mandatory chit, it must be played at his next combat. So what happens is:
1. He throws it back to the cup and draws hopefully an eligible chit. 2. He passes it to his Western Ally, "forcing" him to play it during his next combat. 3. Since it's a mandatory chit he doesn't throw it back to the cup, but cannot play it in combat either since he has no french units. So he just throws it back to the box without resolving it in combat. 4. He plays it nevertheless even with a non-french unit, since it's mandatory.
As i see it, none of the above statements is correct but i really can't imagine what is.
We just played for the second time this past weekend. Our understanding of the rule is that the Eastern Allied player may hold on to the "bad" chit. This means that it counts against the total of 3 chits that the Eastern Allied player may hold, but it also keeps his ally from drawing that bad chit. So I agree with Carl Sonson!