This has been checked on the demo and the sandbox.
When using the advanced search to find contacts by event name, attempting to tag contacts results in all the contacts in the database being tagged. Here are the steps on the sandbox:
- Go to advanced search
- In the events section, enter Rain-forest Cup Youth Soccer Tournament in the event name field, click search
- Select All 6 Records and Tag Contacts, click go
- Select a tag and click go
- All 107 records get tagged
So far the only time this happens is when searching by event name. I haven't had this happen with other fields yet, but I haven't tested them all either.