A couple bugs I've found in this:

The "Win/Loss" scoreboard actually shows wins/total games. (So if you win 4 matches and lose 1, it will say 4/5).

Related to the previous, quitting out of a match in progress increases the Loss column by 1 even though you didn't lose. And since there's no way to restart a level, trying repeatedly for a 3 star rating on a difficult map can rack up a large quantity of "losses."

The ballista turret can sometimes get stuck turning in nonsensical ways, like continually turning clockwise to track an enemy that's moving clockwise across the field of fire (around a curve) without ever actually pointing at it enough to fire. This is particularly noticeable when you have the fast-moving enemies and the turret is placed on the inside of a curve in the track. (Which is the most logical place to put it.)