To recreate the issue:
Copy the setup as seen in the image, the barrel above the track contains any item, the other barrel contains 3 unstackable items. The track is facing east (the same setup facing south will not cause this bug). A hopper minecart needs to be sent of from the 5th powerd rail as measured from the curved rail. When it is under the barrel the curved rail changes direction as it should, however the minecart bounces back.