Yeah, I've seen the turret bugs you mentioned. The best way I've found to avoid the last 2, is let go of the fire button as soon as the finished turret appears, cause there seems to be some kind 1 to 1 1/2 second period after finishing a turret(built above eye level) where this can occur. Either way, these bugs don't effect gameplay that much. The extra floating tripods are a bit of an eyesore, but its really not a big deal.
As for the weapon construction bug you mentioned, I haven't encountered that personally. Remember(and please all you U4E vets out there correct me if I'm wrong) that you can only build 3 different weapons(one of which is always a phasor powerup) in a certain length of time(I'm not sure exactly how much time it is, somewhere around a minute). After which one of those possible weapons changes. Also if you have already built one or more of the possible weapons(excluding phasors) in that timeframe you cannot build anything else until the next timeframe comes up.