Steps to reproduce:
1- In creative mode, create a loop of track that includes a short diagonal section running southwest, followed by a straight section running two blocks west, then a right turn into a straight section running north
2- Place a Furnace Minecart on the loop south of the diagonal section of track
3- Facing south, right-click on the Powered Minecart with charcoal
The Furnace Minecart proceeds along the track as normal until it reaches the short section of track running to the west, at which point it 'bounces' back and forth between the two corner pieces of track.