When you are inviting users to topics you get notified and a green banner lets you know the user has been notified. However this is staying. The only way to get rid of it is to refresh the page. Using the latest version of Discourse I can repro here and on another site.
Repro:
Go to a topic and invite a user
Go the another topic and try to invite another user
I’m unable to reproduce this issue in my local development environment using both Chrome and Firefox in Ubuntu. Also, I’m unable to reproduce here in meta using Chrome in Windows.
@ondrej & @Ronny_Gil are you still facing this issue here in meta/try? May I know which OS and browser you’re using?