I knew about commenting, but I'm really surprised that you can make posts too. That would be like posting to the Local feed on another fedi server. Wild
Do you mean like another kbin instance? I haven't tried to connect with another instance, but when you attempt to start a post/thread/link [etc] it usually tries to create it in the magazine you are currently in.
What instance are you attempting it on?
Edit: Looks like it works fine - Just make sure to navigate to the instance+magazine you want to post in, and the + button will add your submission in that place.Syntax for viewing/posting on another instance within your current account; treat it like a magazine, with the domain name added: