Sometimes can't see turrets upgrading

Sometimes when a turret is upgrading, I don't see any indication that it's being upgraded. It just looks normal, except it can't be damaged and doesn't shoot anything. Pretty annoying when I waste juice trying to destroy a turret that can't be touched.

Maybe if the turret is out of rendering range when the upgrade starts, the upgrading graphics won't show up once you enter range? Just an idea..

On a related note, I don't think turrets should be completely invulnerable while upgrading. Maybe some reduction in damage taken, but invulnerable is taking it too far

But the turret upgrade animation puts an explosive proof barrier between the turret and you! That rocks :-D