Every once in a while the tool holder on my changer gets in the situation as shown in the picture. I'm not sure how this happens, The picture makes it look like there are flats on the "Teeth" but up close I don't seee any. This has happened with almost every tool holder I have (12 Total), and no particular position in the tool rack. The spindle can spin freely and tools can spin in there forks (But does take a little effort). I have no idea how this happens.

I need a way to detect when this happens. At the top of the spindle the drawbar goes up, but acording to the drawings there is an internal spring, so the "drawbar in position" sensor returns true.

Any idea on how I can detect or prevent this?