Fleet mechanics + movement mechanics = suck.
The problem lies in an equation, how do I get there the fastest. Your ship looks at it's position and says, hmm, it takes me this long to accelerate to full speed, and this long to turn around. If I start booking it, I can be clipping along nicely by the time my wide ass gets turned around. Of course, I'll also be over there...
The question then is does over there pose a problem. When turning to face an opponent right by you, the idea is to stay where you are, it entails at most a 180 degree turn. To circle around and face your attacker would be nearly twice the angular change depending on the relative positions. When your target is out of range, you have to move into range as well. Your angular requirements will be roughly the same as your arc wont change the radial requirements that much, but you'll be at full speed when you reach the proper direction.
In other words, it's faster to behave stupidly and run through the mine field. Fleets of course make this a horrible mess by throwing in screwball allignments and move paths that further destroy any hope of reasonable movements. To solve it, one has to have the angular momentum strong enough to minimalize turn arounds, or write a movement AI that's either insanely brilliant, or insanely ineffective. Probably ineffective.