my two roman armys are under attack by 4 parthian armies (Sassinid persia's gang of eight satraps have amazingly taken up Attila's destiny of rampaging across the steps before Attila has even come to power

)
naturally I want to retreat to the city I just took (The mighty capital of the Lugians: Belz. has a nice ring to it don't you think?) which has another two of my armies stationed there and next to it. One army retreats to the city. good. the next army wanders off into the forest and is now surrounded by 4 parthian armies which of course, the ai being the cowards they are, gang up on it and seek to destroy it. Rage quit and try again and see if it happens again. of course it does, exactly the same way.
why is Varus not leading his army back to base but instead wandering off into the forest? and why does this still exist in 2015 after 15 years of total war?
and totally offtopic, but why does nearly every battle end up being fought in the exact same looking forest? the landscapes seem even more generic than rome 2 and thats saying a lot.