Yeah, I found tidy up units box, now unchecked. Now I can do what you suggest when units are not at full strength but are with units of same type. The problem was that the Princes unit had 4, the other was a full 40. Dropping the 40 on the 4 didn't work, it didn't transfer the men. Course I kinda knew that wasn't gonna work, but I had to try.

Tidy up units baaaaaad.......