The problem you have is using radar to detect ground targets. There is naturally ground clutter that will show up. The question is, to you program the software to be very smart and edit those contacts out, and take the chance that an actual target is missed, or show everything and take the false positives it produces. Kind of a rock and a hard place situation, and most developers opt for false positives over false negatives. False negatives could kill.
For aircraft the solution is simple, use transponders. That is why civil radar sites rely on transponder equipped aircraft. They still have the ability to show actual radar returns, but there are too many false returns. The problem with the ground radar system is, not all vehicles are equipped, and you are also looking for the errant vehicle that may not supposed to be on the airfield.
What a load. Look, ASDE-X alerts on false targets. It had been known to alert on blowing leaves/grass/whatever. The less than desirable part is that it HAS missed aircraft crossing hold short lines. It is NOT “zero-fail.”