Mmm. Looks like you've stumbled across (or at least highlighted) a bug in the way kbin federates out links in it's content. I thought I'd covered the various cases but apparently didnt.
When a post is made to kbin (or federated into it) that contains !magazineName@instance it does a best effort to make links that will work for users on that instance, but it appears that best effort applies to the outgoing federated content too - and it shouldnt, or at least, it should do something different.
I'll get a bug ticket in.
EDIT. For now I'd recommend that where possible you use fully explict links i.e. [{@|!}community@instance](https://instance/{m|c}/community)