I'm guessing this is a display bug of some kind. The 109th fortified zone should have surrendered when forced to retreat but it's not showing up on the list. The Soviet casualties are not large enough to indicate a Soviet division actually surrendered (and an attacking unit should never surrender in any case). If by any chance you have a save before the attack and can try again, let us know.
All understanding comes after the fact.
-- Soren Kierkegaard