Army stuck in fort

[Cultured Drizzt fan]

Well something weird just happened, and I think I may have just lost one of my best armies.....

I am the British, and have been at war with France for a long time. I moved my army into the Artillery fort just east of Paris and ended turn. The french army attacked, I destroyed them and they were sent running all the way across France. There is no army in Paris, so come Savoy's (my Protectorate) turn they invade and take Paris. My turn, and France has been destroyed. I go over tom my army and they are still sitting in that fort...... and I can't take them out. The animation is that of them being in a open field, and they cant move or do anything.

anyone else had this problem?