Parent Category Behaviour

Go into Admin / Display / Content Menus / My Menu
Click waste basket on Parent Category.
Parent Category clears.
On save Parent Category changes to the top category 'My Shop'.
That's a reasonable default.

Go to corresponding shop page.
Get errors in category listing.php due to $this->element being null.
I think $this->element should be checked before use.

However, if I go back to admin, clear Parent Category then change it to 'My Shop' using the 'Select' button then it works OK. Looks like there might be something wrong with the default handling.