The part Probodobodyne RoveMate has circular mounting points, while the model is square. This makes it difficult to mount wheels, or other parts, as the more you stray from the center, the more of an angle the part is placed at.
Sorry if I don't use the right terminology. I am not a programmer/modeler/developer. I just play the game. However, the picture illustrates the bug fairly well.
Edit: I noticed that if Snap is off, it mounts properly. This seems to be an issue only with Toggle Snap set to On.
KSP v. 1.1.2 Steam PC. Win 8.1.