There is a process lag in fort battle updating in all cases. The most obvious one is when you relog you do not see ranks in battle chat for a minute or so. Keep this in mind when you place your dot & target (2 step process you MUST set target. Target yourself if you do not want to move). Cancel target arrow after battle begins if online.). Next due to the lag you MUST keep fort open for at least 1 minute (2 minutes with slow internet) after placing your dot & target. Finally check back in a hour or so to first make sure you have not been stacked (remember the lag? Yep 2 place dots at same time, neither see each other) & also that your dot is still there.
Basically, you rush in, place dot, close fort and your dot will not be STUCK.
Also, keep in mind that this lag can also affect your late stacking. You move your dot, the game needs time to process the request. You stack less than a minute until battle starts, you are asking for trouble, ie no stuck dot!
ATTACK ~ No stuck dot and the AI will put you anywhere & this means usually the wilderness far away from the group and you will die horribly & quickly.
DEFEND ~ No dot and the AI will place you somewhere on the fort. Clearly not as bad as no stuck dot on attacks.
EDIT: If you have ranking screen due to either script or being an officer, you CAN trust your dot you see on ranking screen as STUCK, just not the original fort screen.