Isolation question

[CountryBoy]

I reloaded the past saves and this is the sequence:

At the start of the German turn, Turn 10, it looked like this - the units were not isolated and the bridge was intact




At the start of the German turn, Turn 11, it looked like this - The Russians had blown the bridge during their Turn 10, the units were not showing as isolated.



At the start of the German turn, Turn 12, it looked like this - the units were still not isolated (the screenshot looks the same as no units moved). Surely at this stage the Russian units should be isolated?



At the start of the German turn, Turn 13, the units WERE now isolated.




So the Russians blew the bridge immediately prior to the German Turn 11, but the units didn't show as isolated (from a German perspective) until the start of the German Turn 13. Isn't that one turn too many or is it normal?