deleting item kills gb2

complicated...
was testing the "weight by points" category.
1 - added "weight by points" category to a site @ 5% course grade.
2 - got 5% overage (site was already 3 cats @ 50%, 25% 25% and an extra credit cat)
reduced a 25% to 20%
3 - added 50 point item, 20 point item and 5 point extra credit item to "weight by points" category
4 - I thought the %category weights were screwy so was explaining to David WHY and decided to
start from scratch adding the items.
5 - deleted the 1st item just fine.
6 - deleted the 2nd item and couldn't...got popup divide by 0 error I think.
7 - refreshed and could no longer access my gradebook - got blank gb and popup w/divide by 0 error.
8 - told Mike W. he fixed it but sort of trashed the gb, ec category was gone.
Mike said try and repeat it and if I could, do a JIRA.
9 - ANYWAY..set it up again, the same way, adding the ec cat and put its Unassigned item back, adding
the "weight by points" category and items.
10 - deleted 50 point item fine...again
11 - tried to delete 20 point item and got divide by 0 error. selected delete again and got "Failed to update item: You
cannot include a deleted grade item in grading. Please undelete the grade item first.
12 - tried refresh again and got blank gb page w/division by 0 error.
13 - Mike said do JIRA w/screen shots but I'd already lost the error messages except the one on the blank page.
it is exactly "Request failed: Division by 0:"