Just like I tell my end users at my programming job - computers are dumb. They will only do EXACTLY as you tell them to do. Voltaic Sentinel has been "told" by the original Devs to loosely follow behind a player and automatically attack any enemies within its range at all times. If you summon it, that's what you should expect it to do, at all times. It's reliable, but incredibly dumb. But you always KNOW what to expect from it...
It sounds to me like the issue here is Blasters not being Blasters... considering the fact that it trails BEHIND you... if your Voltaic Sentinel is randomly attacking mobs and causing you unwanted aggro, then it's my belief that you're not making effective use of the RANGE of your powers... sounds like you're right in the thick of it to me. If you want to play that way, fine, but then don't be surprised when your sentinel attacks the next mob because they are within range. That's what it's programmed to do, it written right on the tin. You've got a choice - either sit back and use your range (which is why people choose ranged damage classes to begin with, usually!), or get in the thick of it and DON'T take the sentinel, because it clashes with your play style.
Or, I guess you can ask the Devs to completely reprogram a power that's worked fine for most people for years because it doesn't match your personal playstyle... I guess that works too!