Can't reproduce...

Seems to be working again. Probably a deployment gremlin. Again. :-(

Reproduced it today following these steps

1.Open a page with VE
2.Go to Page Settings option>Categories
3.Type a category name in the text field
4.When the drop down box appears, close the dialog
5.Again, reopen the Page Settings option>Categories
6.Now select a category from the drop down box

Observed Result:

It gets added twice,if you cancel the dialog box again it will throw the error:
TypeError: categoryItem is undefined

If you reopen the Page Settings option>Categories, you will get stuck inside it.

Change 151088 had a related patch set uploaded by Alex Monk:
Tear down meta dialog pages when cancelling

https://gerrit.wikimedia.org/r/151088

The patch is not even merged yet, assuming the bug was closed by mistake.

Change 151088 merged by jenkins-bot:
Tear down meta dialog pages when cancelling

https://gerrit.wikimedia.org/r/151088

Silly Gerrit.

This is still happening on Betalabs

Can now successfully reproduce on deployment-prep, but not my local wiki...

Also, I am getting a different error this time while closing the dialog second time:
Uncaught TypeError: Cannot read property 'disconnect' of undefined

And I can't reproduce it on deployment-prep any more. Rummana?

Hmm, I can't either. Marking it as fixed.

Verified the fix in test2

Verified the fix in production