There is currently an intermittent known issue with the category selection where at times the message 'You must select a leaf category' displays at the end of your selection path when attempting to choose a category. Our engineers are aware of this issue and are currently seeking a solution.
When this occurs you can typically navigate away from the category selection area and then return to it to try again and if needed you can also clear the cache of your browser after saving your listings and try again.
We will update this thread as soon as more information regarding this issue becomes available.
Apologies for the inconvenience.