SO edit form. After decreasing line item the Qty and status is calculating incorrectly

Steps

1. Create new SO, add some Item Qty 4 -> Use in Stock
2. Save&Process SO
3. Reopen SO and increase Qty to 7(PO Request) ⇒ Save
4. Reopen SO and decrease to Qty 3
5. Reopen SO and look at the Qty and Item status

Expected result – Item Qty should be decreased to 3, Item status should be Ready to ship

Actual result – Item Qty  is decreased to 4, Item status is Pending PO