I noticed this when I was trying to pull data from the entry using $CATALOGUE_ENTRY_FIELD_VALUE; it did not return anything.

I suppose I could just duplicate the custom fields on the satellite site, but that can be annoying as you can imagine.

Similar to custom Comcode tags, even if the satellite site doesn't have a specific tag that's being used, it's still capable of pulling it from the central site -- if this could work with these custom catalogue fields, this would be cool.

Sorry, we can't support it easily. I'll add a new issue, but otherwise I've handled this as a documentation problem.

This is what the docs now say:
"Custom fields on forum content are not supported across networks. If you set them up they'll only be viewable for the particular site that content is added/edited on, and not show up on other sites."