Screencast at http://youtu.be/EbQoK4-3saI

Screenshot

Cannot reproduce.

I can reproduce it, both in beta and test2. The step#5 is the key.

Reproducible in beta ad test2 - but multiple categories do not get saved, so the bug is minor.

Steps(simplified):

1. VE - Categories - click on a drop down for an existing category and enter some value. Hit Enter(important!).
2. Click Cancel.
3. Open Categories again - there will be two instances of the category displayed.

Yep, managed to reproduce this now. Thanks.

This appears to be due to MWCategoryWidget#addItems using promises (the parent GroupElement#addItems does not really support this) - that callback may finish running after the user has already cancelled and reopened the categories dialog.

I can still reproduce it,the steps to reproduce are same as above.See screenshot.

OK, I ran through the exact instructions given above in both Chrome 39 and Firefox 35, and couldn't replicate. Could you tell me how to replicate it now?

I can't reproduce either, but the buttons definitely act funny, visibly disappearing and reappearing when the popup closes. Some refactoring probably wouldn't hurt and just might fix this issue.

Steps-:
1> Select Categories
2> Add a category(one which lacks a description page. When added, category name would be in red font color)
3> Click on the indicator-down arrow.In the resulting pop up enter a name in the “Sort this page...” input field. Hit enter to set the value.
4> For the same category, click on the drop-down arrow again and in the resulting pop up enter a different name in the “Sort this page ....” input field. Hit enter to set the value.
5> Click on the drop-down arrow .
6> Click Cancel.
7> Select Categories.The category has been added multiple times.

Screencast at http://youtu.be/cVLFH4QOMzU.

Oooh, the big dialog's "Cancel" button. I can reproduce now.

This now seems fixed-ish (no duplication of the category), but the newly-added-categories are still retained in the dialog (but not inserted) if you cancel the dialog. Instead, on setup the dialog should clear any new-and-not-yet-put-into-the-document categories.

I can't reproduce this now. I followed the exact steps in the screencast and the category dialog ends up empty. As it should, since I clicked cancel. If I click apply changes instead, only one category is saved. I didn't manage to reproduce duplication anywhere.

Perhaps one of Alex's recent changes fixed this?

Might have been the fix for T89923.