Steps to reproduce:

1. Add Dashboard problem widget and save changes.
2. Now, switch to Dashboard edit mode and open widget 'configuration' window.
3. Add host groups, excluded groups and hosts as much as possible to make window content scrollable.
4. now, scroll till the bottom and try to add some tag.

Result:
although I clicked on 'Add' button, actually the checkbox of severity was selected. This doesn't occurred always, but I was able to reproduce it several times. See attachment.