You cannot ride through a nether portal in a Minecart, and if you are playing survival you will most likely get stuck if you try to do this. Instead you should be able to transport into the Nether with/without the minecart.
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Duplicate of MC-67 , please use the search function to see if your bug has already been submitted. Currently over 35% of tickets are being closed as duplicate.
Already a bug. Already resolved.
Read through the comments of MC-1969.