I found the problem. After the army is selected for a sync move, it must be actually moved. Then you can go back and either hit the delete key for the corp that is to stay behind or drop its tab back in the region of origin. What I was doing before was trying to delete the corp move before actually ...

I tried that but the corp still moved with the army. Any other suggestions?

Thanks and regards

Maybe I'm missing something but when I order an army to sync move and then try to leave one corp behind I can't seem to cancel that corps move. In fact when sync move is selected at the army tab it automatically gives the same order to the corp even though the individual corp buttons for sync are no...