MMBE, stock at plan level doesn't match

When using MMBE to check the inventory, I got following result for unrestrictied use. The total quantity at plant level doesn't match with its detail. Stock provided to vendor is not added to plant stock.

▼1000 Werk Hamburg 158

　・Stock Provided to Vendor 20

　・0001 Raw Material 148

　・0002 Finished Goods 10

The explanation for this problem would be that stock provided to vendor is managed at plant level, but since the physical stock is already at the vendor site, it's not unrestricted use anymore and should be excluded. Yes, but since this t-code shows the detail of the inventory as drilldown, this appearance will lead to misunderstanding.

Is it a bug?

Anyone has any idea to fix it?

Regards