Back in June 2019, runpunkrun explained how to use the at-sign to create Dreamwidth user heads. Two weeks later, I explained how to use the at-sign shortcut for other sites as well.

runpunkrun found a bug when the at-sign is followed by a period.

To test that bug, I created the usershortcutbugs comm. It ran through all the possible issues with touching punctuation, and I filed a support request:
https://www.dreamwidth.org/support/see_request?id=40486

BUT

The new code push has changed how DW interprets the characters. Due to changes in my impairments, I'm no longer able to bug hunt. I'm hoping someone reading is willing to take up the cause.

After the latest code push, the escape character for at-sign stopped working correctly: backslash preceding the at-sign turns off formatting BUT the backslash also displays. (Check out my link above and you'll see some ugly crap!) The new code push also changed how usershortcutbugs displays.

Care to step in? I'd be delighted to provide access to usershortcutbugs if that helps.