Wrong error message text when updating 999+ problem events

Steps to reproduce:

1. Change "Rows per page" in user profile to 1000
2. Go to Monitoring -> Problems
3. Select 999+ problems
4. Mass update events
5. Select "Acknowledge" and fill in "Message" field
6. Click update

Result:
message "At least one update operation or message is mandatory". I assume there is a limit, and can update only 999 problems

Expected:
correct message text of the problems update limit