Selecting a single turret by clicking correctly selects the turret. However, drag-selecting a turret treats each of the 4 blocks of space taken up by the turret as individual turrets. Selecting "half" the turret gives Auto-turret x2, selecting all of it gives you Auto-turret x4. The effect extends to drag-selecting multiple turrets, giving x8 for 2 fully-selected, x16 for 4 fully selected, etc. When selected this way with incorrect number of turrets shown, it is impossible to turn them on or off.
Thanks for reporting.
This bug was already reported under another name on mantis. And as far as i can see fixed (-:
Oh, I'm sorry. I hadn't looked through the Bugtracker thoroughly enough.
Np at all it was noted under another name as it happens to more objects (-: