Ya, it's caught me off guard a few times. I have my unsheathed crossbars on 1-4 and my sheathed crossbars are on 5-8. I put my "auto-sheath" preferences on 5, because I've noticed sheathing and unsheathing will automatically put you on which ever bar is active in numerical order. Because of this, I've put the stance command on crossbar #5 so I can switch back quickly in a dungeon.

What I've wondered (and admittedly haven't looked very much in the options menu) is can you turn off the "auto-sheath"? I just want it turned off so I can be "weapon drawn" the entire time. Not a huge inconvenience though.