Forge registries support a unique feature called registry substitution. Some mods utilize registry substitutions in order to avoid coremodding. Railcraft substitutes all vanilla minecarts except the spawner minecart. As a result, the minecart spawned with the MinecartInteraction feature are incorrect and leads to weird issues. My suggestion is to spawn minecarts through entity registration or entity entry's factory instead.

Related: Railcraft/Railcraft#1110

P.S. The instanceof check for EntityMinecartEmpty is somehow funky too; a bed cart added by railcraft can be replaced to be a chest cart. This detail is up to you to decide.