Regardless of what direction a player faces initially, boarding a minecart forces their head to face south. This is an issue on all devices tested so far, on Bedrock edition and has been an issue since 1.14.

Here is a video demonstrating this bug in action - https://www.youtube.com/watch?v=eCNHmJoHNs8

This bug also affects rideable mobs, but does not affect boats.