Messing around with rails, placed a minecart on powered activator rails and tried to enter it. When I entered, I was in the floor. After trying to recreate it, I found that it didn't happen every time. Basically, the steps are:
Place down activator rails.
Activate the rails with a lever.
Place a minecart on the rails.
Enter the minecart.
If you are not clipped into the floor, repeat step 4.
If step 5 yields no results, exit and re-enter the world and repeat step 5.
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We're tracking this issue in MC-263712, so this ticket is being resolved and linked as a duplicate.
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