Robot mysteriously stopping and backing up

[TubaMorg]

I've never heard of a library bug like that.
Without being able to see your code, the first thing I would check for is to make sure your motor signals aren't over ranged. This will cause the motors to reverse in some cases.

[DavidGitz]

When we were first testing our line tracking, this happened briefly. I attributed it to a low battery (it was about 11.5 when it wasn't moving), so possibly one wheel was moving and the other one wasn't, and since we are using high traction wheels it caused the whole robot to drive backwards. After replacing the battery with a fresh one, this has not happened again.