Small issue I noticed today on my forum.
If you embed a tweet with a large number of mentions in the body of the tweet, then those mentions are screened to see if they pass the total number of allowed mentions in a post. Obviously, they aren’t real mentions because they are links on twitter, not links on Discourse.
e.g.
gives me this error
I assume that shouldn’t be the case, but it’s hardly a big or frequent issue.
I also ran into this issue when I was posting a list of 14 group members’s email addresses.
I had to up the allowed count past 10, posted, then put it back.
It would be great if the process that counted @mentions could look to see if they matched real users, or ignored them in quoted text (where they don’t work as mentions anyway)
Thanks for reporting that issue. I just pushed a fix to make sure we don’t count mentions in oneboxes 
https://github.com/discourse/discourse/commit/80f258e51c102cf0fa746a9692f0cccae1c1afac
