First question, on the Project Definition what inventory indicator have you selected, Valuated Stock, Non-Valuated Stock, or No Stock?
For the Account Assignment on the PO there are 2 choices for using WBS Stock Segment, P or Q. Which one you use is dependent on the stock indicator on the Proj Def.
Then when you are receiving material you can GR it into Unrestricted or Quality Stock. This Q stock is not the same thing as the Q Account Assignment indicator.