Coureurs de bois have "can hide in woodland" in their descprition. For some reason, post 1.03 they seem to be unable to hide in the woods... I can place them in open field and they hide just fine, but not in the woods. The same applies to north american native axemen (the lowest level native unit colonial powers can train in Americas): they can hide in plain field, but not in the forest. I suspect, some terrain type flag is messed up.

I suspect other units are affected too however native musketmen are able to hide in woods.