While investigating issue 251376, I managed to hang a form with client side validation.

I created a new issue in my tracker with a bogus value for an issue multi-link.
The title was set to required, but was empty.

I clicked on the submit button and it was disabled as expected.
However, the form validation flagged the title as required.
I then entered a title, but the submit button was still stuck as disabled.

Refreshing the form cleared the disabled button, but was a pain and could lose info
(like an uploaded file).

Adding a routine to re-enable the submit button is needed.
The code that disables the submit button can add a setTimeout call to re-enable
the button after 1 or two seconds. This should be enough time to reload/refresh
the page.

If the page is not refreshed, re-enable the submit button so the form can be 
submitted again on the theory that something went wrong with the submission and
the user needs to try again.

If the page refresh happens before the timeout, the routine is destroyed and never runs.
Two seconds sounds about right for the submit to complete and start the reload.
If there is an error displayed by validation, the user will probably take more than
two seconds to understand and fix the issue. So the form is ready to resubmit
by the time the fix is done.