[Edi]

This sounds like a transient bug that affected early versions of Dom3. I only saw it once myself, but then it happened quite consistently to my friend who I was playing hotseat with. His Marverni commanders kept randomly dropping units after a move, so he had to check every turn to make sure they were still there. This was with 3.04. Never seen it since.

What version are you using, what nation are you in the game and what other specific can you tell me about it (commander type etc etc)?