yeah; its a really weird bug i think they'll fix in the next patch. oddly enough, i've only had it happen a couple times, but all had about the same conditions:

Me as Prussia
Enemy as Marathas
Battle is in India

Playing any other faction that has never happened, but then again Prussia is the only European Faction I've taken into India. Which is strange considering I've played U.P. and GB campaigns (obviously got bored and didn't finish)