See my post here as to why it happens: http://www.swtor.com/community/showthread.php?t=248893 Generally, just have ONE person designated to the turret, and you shouldn't have too many issues.

Greetings, To the Devs it may concern, and other players, I have found out through some thorough testing that the reason the stationary mountable turrets on Ilum (in my case, the Republic side, as there is a heavy population imbalance towards Imperials on our server, and we depend on them to defend our base) is due to two things: 1) Being dismounted via stun or knock back immediately upon mounting the turret (as soon as the timer fills up all the way). 2) Rapidly clicking on the turret and moving away from it, and attempting to use it multiple times. As a result, it usually isn't even a day or two before ALL of our stationary guns are rendered inoperable on the Warriors of the Shadow Republic side. We must then wait until a SERVER RESET before any of them become available to use again. Could a possible fix be implemented for this in the future? Perhaps make the turret un-interruptable, or at least make the transition into mounting it much less buggy, and less likely to cause the turret to despawn? Thanks!