Deleting a group with collections submission does not really release them

I've tested this in Mahara 15.04, in 16.04 and the latest one (Nightly).

Here is a description of the bug and how to reproduce it:

1. I have a group with collections that have been submitted for assessment.
2. I delete that group without releasing the collections.
3. When I go back and check with each users that had submitted a collection, I can see that my collection is still considered submitted... in a deleted group (cannot access that group anymore, normal, but the link remains indefinitely).
4.As the same user, I can still modify the pages of my collection without problems. The BIG problem comes when I wish to submit that collection again in another group. I can't because the system still thinks that it has been submitted in the deleted group. it gives an error message (access denied type of error).

This is a big problem for our institution because we ask our teachers to delete their groups when they don't use them anymore. Some of them still have collections submitted for evaluation and the teachers sometimes don't bother checking before. Note that this problem only affects collections and not pages.

I don't if anyone else came across this behavior... Thanks for you help as always :)

Melvin