That stupid bot is such an artificial difficulty device.
I can't travel the levels as fast as Descent 1 because of that bastard, sometimes it seems like a stop n' go thing;
LOL i know what you mean haha XD at least it has this buzzing sound to show that it is nearby. I hated that little bugger so much but it adds a bit of fun to the levels.
Nothing like fighting your way through a cave then all of a sudden your afterburners are gone, or your missiles, or guns.and then screaming "WHAT THE F***!!!!!!" lol XD
What I usually do is sit and wait for it, let it come to me instead, and unload on it with the Vulcan Cannon or better yet the Gauss cannon. It can outmaneuver most missiles, even homing, so save on that but mercury missiles do well. stunning it with flash missiles mmight work. Sometimes there is a lucky break where the thiefbot will go into a room with just one exit so you can trap it by being at the door and just shoot up the thiefbot whenever it comes near you =D