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: