Manipulating messages in dropdown

Go to the inbox, mark the message in the radio box. Select "Delete marked". That action gives me

"The submitted form was invalid. Try submitting again"

Looks like a bug to me and not a feature. I tried it on a few updated boards that all work perfectly, they had the same issue. All boards tested are on different operating systems, all using different versions of php (7.2,7.3,7.4).

Topic:

https://www.phpbb.com/community/viewtopic.php?f=661&t=2535026