When running ATH tests agains Jenkins 2.7 the New Item Wizard fails to enable the OK button after the name is inserted and the type of item selected.
Some investigation and debugging showed that:

1. the item name is inserted and stored with jquery, no warning shown. Validation of OK button fails cause the item time has not been selected yet (OK button not shown yet).
2. the item type is selected
3. right after selecting the item type a red warning is show on the item name input text ("The field cannot be empty, please enter a valid name")
4. the OK button is not shown case now the validation fails on the item name (empty).

If while debugging, you click anywhere on the page after the item type is selected, the red warning goes away and the OK button shown. Sending Keys.TAB with selenium (or changing focus) does not work instead.

Looks like this condition is false https://github.com/jenkinsci/jenkins/blob/5f9614433ec3bd9057097bbe2af7d445e6cd918e/war/src/main/js/add-item.js#L178.

The ATH tests are failing here https://github.com/jenkinsci/acceptance-test-harness/blob/master/src/main/java/org/jenkinsci/test/acceptance/po/JobsMixIn.java#L25