Purchase Returns against Purchase Receipts

ERPNext
1

I’m using Frappe Framework: v15.89.0 (HEAD)
ERPNext: v15.89.0 (HEAD)

I created purchase receipt with accepted qty= 1000 units
I performed 2 purchase receipt returns against the above purchase receipt (-50 and -80 units simultaneusly) 1000-50-80=870

Now created Purchase invoice against actual Purchase Receipt, system fetched units 920 at purchase invoice (rather than 870)… entertaining only 1 purchase receipt return…Pls check is there a bug or setting matter?

Tested also at Framework: v16.0.0-dev (HEAD)
ERPNext: v16.0.0-dev (HEAD) Result was unexpected.