Wppost in combination with wordpress plugin hubzilla_wp has issues
Edit: as of early September 2019 the Hubzilla to Wordpress post functionality seems to be broken. Comment cross posting and Wordpress to Hubzilla still works.
I added both the wppost plugin to Hubzilla and the hubzilla_wp plugin to my Wordpress, and it seems to work fine to post and comment from Hubzilla to Wordpress.
However when I post from Wordpress the post gets created in Hubzilla and then posted back to Wordpress, where it thus creates a double post.
Similarly, if the user that made the original post on wordpress (can be different ones as long as it is the same) makes a comment, than that comment also gets posted on hubzilla as the channel owner and them immediatly pushed back to Wordpress and thus duplicated.
Somehow the wppost plugin seem to miss a check if the post/comment was done via wordpress and thus not send it back to wordpress.