Placing a rally banner inside the Arena makes it unusable
Shame http://brightrockgames.userecho.com/topics/1269-you-can-place-a-rally-banner-inside-the-prison/ got closed, as it also can suffer. If you place one inside the Arena, all units inside will be pushed out. Additionally, you can't place any unit inside while the banner is there. It can cause a good grief if an enemy unit escapes thanks to a mishap with a banner.
Hey ZzZombo,
Just to let you know we really appreciate you reporting all these extremely minor issues, although some of them might not be considered an issue or may in fact be working as intended there are a few which are indeed issues that simply have been overlooked, missed or never reported.
It'd be really great where possible if you try to include steps to replicate, although I can often conclude steps to reach the same issue as you from your descriptions it's just nice to have in addition.
With regards to this one it's quite a small issue but let me explain what's happening. When a rally flag is placed for a unit that is in the Arena the unit will attempt to respond to the flag, as such it will leave the Arena, however the flag being placed in the Arena still causes this behaviour, but of course due to the same reasons as the prison the flag cannot be reached.
This means enemy units that are in the Arena will not be affected because they will not respond to the rally flag, likewise they cannot respond to their owner's rally flag if they are in an enemy Arena.
While I'm inclined to write this off as working as intended I'll see if maybe we want to change the mechanics so that if a rally flag is placed that is unreachable units do not leave arenas. I can't guarantee that will happen but I'll look into it.
Cheers,
Lee