It is not, maybe it has something to do with the client or the instance from where you see it, here is how it looks with Sync for Lemmy and Lemme instance...
It's what happens when content is url encoded and not decoded again later. It's easy to do by accident because you can't tell if a string is already url encoded in any general way, so the processes responsible for sending and receiving need to agree on how/when to encode and decode (i.e. they both have the power to break it for the other)