ATH core.CreateItemTest.duplicate_item_name_displays_error has detected a regression in Jenkins core as the "OK" button is no longer disabled when the name is a duplicate.

reproduced manually

Steps to reproduce

build and start Jenkins in a clean Jenkins home
skip all plugin installation
create a new Freestyle job called "test"
save the job
go back to the root and create a new item
enter "test" as the name, and select Freestyle job

Expected behaviour

the form validation shows the name is not good
the OK button is disabled

Actual Behaviour

the form validation shows the name is not good
the OK button is *not* disabled