If minecarts are spawned multiple times on the same track, then pushed off the track, they will float and continue in a random direction unless bumped, then they will change direction. However they don't float in mid air, they sweep down and continue floating in one direction without getting slower.
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Duplicate of MC-14 and MC-12526, please use the search function to see if your bug has already been submitted. Currently over 57% of tickets are being closed as duplicate.
This is different, without a slope, and dosn't float in evry direction.