I was playing with friends on a realm and we wanted to build a railway to each other's house.
While putting a minecraft on a powered activator rail, the minecraft started to wiggel and didnt allowed any player to hop in.
You can get in on a normal rail, but as soon as the minecraft rides above a powered rail it throws the player out the minecraft and wiggles, it ends instantly after it get back on a normal rail.

After a several testing, it doesnt matter on which block the powered rail is, it begins as usual to wiggle and so on.