Steps to reproduce:

1. Create host, items, trigger and generate a problem;
2. navigate to problem view and press "Update";
3. refresh the page (if asked for confirmation, leave the page);
4. same acknowledge window is opened without the main page. Just the popup;
5. change something: add comment, suppress problem or change severity etc;
6. observe the page is reloaded and success message "Event updated" is visible;
7. again press "Update" for the problem and change something;

Result:

Now two success messages "Event updated" are visible.

Expected:
One success message.

Note: 7.0 version doesn't reload the page after problem has been updated, so this issue cannot be reproduced in 7.0.