Forum flag text for "messaging a user" is bugged

[twofoursixeight]

PC/Mobile
Any web browser.

Dimensions or Services it affects
Forums

How often it happens
It occurs when flagging a topic and selecting “Send this user a message” from the flag button, but I believe this is a poor site configuration with the custom text.

Any screenshots or videos showing the bug
On this forum:

On Discourse Try (no bug occurs)

Discourse bug report:

You flagged this topic as Send @[missing {username} value] a message

[popstarfreas]

Never customised that text. Probably just broken in the version we are on.

I updated to the latest version now, perhaps you can check if it is any different?

[twofoursixeight]

Flagged a post as “send this user a message”, still seeing it.

[popstarfreas]

Is it on a specific theme?

[twofoursixeight]

I’m currently on dark theme with sublime_dark color scheme.
I will try it with the default theme, grey amber.
After seeing it, nothing changed. So I’m not sure what happened there.