Comment on Mentions to ActivityPub users
This is not a bug. It's entirely by design, and it has been for many years longer than Mastodon has even existed.
It's how Mike Macgirvin, original creator of Hubzilla, intended it when he created what's Friendica today back in 2010.
It just happens so that Mastodon doesn't expect this and doesn't handle it gracefully. After all, Mastodon is some six years younger than Friendica and, depending on what counts as Hubzilla's start, some four years younger than Hubzilla.
In other words: The Friendica/Hubzilla way of mentioning was here first. Mastodon and its users have to deal with it. Just like with Friendica and Hubzilla having no character limit before Mastodon had 500 characters.
It's how Mike Macgirvin, original creator of Hubzilla, intended it when he created what's Friendica today back in 2010.
It just happens so that Mastodon doesn't expect this and doesn't handle it gracefully. After all, Mastodon is some six years younger than Friendica and, depending on what counts as Hubzilla's start, some four years younger than Hubzilla.
In other words: The Friendica/Hubzilla way of mentioning was here first. Mastodon and its users have to deal with it. Just like with Friendica and Hubzilla having no character limit before Mastodon had 500 characters.
Hubzilla does speak correctly, after all.