Just had this happen to me in my Ottoman Campaign. Admittedly, had it not happened the difference in the result would have been negligable but nevertheless its annoying.
https://img510.imageshack.us/img510/...hroughbuga.jpg
In the above image you can see a large Austrian Army deployed on the Buda and Pest to Belgrade road and my cavalry screen positioned on the bridge that road takes over the Danube (Dunav) River to reach the city.
https://img5.imageshack.us/img5/7642...hroughbugb.jpg
Here is the same area a few minutes later. Note that the Austrian Army under Prinz Eugen is now beseiging the city having walked right through my cavalry screen on the bridge, which as you can see is still in place.
Now the only way I can think that this could have happened legitimately is if the Austrian Army had carefully skirted the edge of my cavalry's intercept zone and crossed the Danube by the bridge further to the east. However, it didn't do that on the map and as you can see it's clearly attacking the city from the direction of Buda and Pest (e.g. the north-west rather than the east).
It would have made little difference to the end result in this case as Belgrade is doomed to fall, in fact tis a strategic trap to draw the Austrian Army into a decisive battle. However, I would have preferred my cavalry to have had the option to withdraw from the bridge, or perhaps even put up a bit of a bridge defence, and if the bridge defence been an serious force I would definately have been miffed.
