Game controllers and minecarts do not cooperate with each other. When sitting in them, all controls revert to default, non-customized settings. Then when you jump out, putting your crosshairs anywhere on it teleports you back into it.
Linked issues
duplicates 1
Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-20463.
Your additional information and observations are very useful, so if you can add them to the comments section of the parent issue it would be appreciated.
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Would you PLEASE do something about this?!? It's been well over 2 months since I reported this, and I feel like it's being ignored.