I have found that, when entering a minecart that is on a powered rail it will dismount me automatically when the rail is activated. It affects me in Creative, Survival, and Adventure modes. I have also tried it in multiple location's, several hundred blocks apart.
Environment
The minecart only dismounts me in the overworld, this does not seem to happen in the Nether. I have not tried it in the End.
Please attach a screenshot with your rail setup