I cannot blow out the candle with a furnace minecart in my hand

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We're tracking this issue in MC-204145, so this ticket is being resolved and linked as a duplicate.

That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.

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No, it isn't. The furnace minecart is an entity and not a block.