Stalingrad and pontoons

[Lowlander]

Constructed a pontoon with two bridging units over a Major river.
When it was completed I deployed the surplus unit to a other location, then moved my first combat unit on to the pontoon, however the far bank hex was RUBBLED so it finished that turn on the pontoon.
Next turn I attempted to move the unit off the pontoon but to no avail its now frozen midstream on the pontoon bridge !!!.