I saw something like this on the ford to the west of Milan - I attacked some rebels there and had a lot of trouble getting troops to cross. Luckily the Rebs declined to defend the ford itself and retreated up the hill into the woods, giving me time to click around and try to get my chaps across..

I found I had to click in the water to the side of the land bridge, wait for the unit to advance to the middle of the ford, then click again on the other side to get them to complete the crossing.

the funny thing was that in the middle of the crossing half of each unit was standing under water with about a foot of river flowing over their heads. plus when I zoomed in the water seemed to be defying gravity by bulging up by the land bridge....took a couple of screenies but I'm too much of a noob to know how to upload them...