This isn't a bug!
You said you are commander at outpost! You are not the commanders of the guards!
To be able to equip guards you have to be Leader, First Officer or Guard Commander! Ask from your leader to appoint a guard team to you! Then you will be able to equip them, relocate them and heal them! But to be able to become Guard Commander you must have at least one point at "City Guards Commander" skill. (More points will allow you to be commander at more teams)
Well, I have a hero, commander of a castle and she can equip guards, stationed in her area without any problem. I had a hero, commander of an outpost, not so long ago and he equiped the guards, stationed there, again without any problem. I believe ariu reported a bug.