This works only with Minecart Experiments enabled.

Steps to reproduce:

1. Place a cactus on sand.
2. Build a railtrack with powered rails, facing into the cactus. The track should be 6 blocks long.
3. Now use a command block to summon a lot of minecarts on a rail of your choice. Push the minecarts in the direction of the cactus. Repeat this step for all 6 rails.
4. Notice that at distances of 1, 2, 5 and 6 rails, one minecart from the cluster survives, continuing in the other direction. Doing this with one block distance can be hard to do correctly, though.

I have tested this bug up to a distance of 26 blocks. It works on blocks 1, 2, 5, 6, 11, 12, 17, 18, 23 and 24.
A video of the bug is attached. Note the similarity to the recently fixed MC-119369.

This bug is also dependent on the number of minecarts in the cluster. Different numbers of minecarts (if low enough) work with different distances, until the number of minecarts gets high enough to not make a difference anymore, where the distances even out to my tested values.

This bug could break many minecart contraptions if left unfixed.

Edit: If filled minecarts like chest or hopper minecarts are used, only every second value of those previously mentioned works (2, 6, 12, 18, 24). 1 might still work as an edge case.