Hi,
this issue has to do with the virtuemart. Actually it is not a problem, it is just how the Virtuemart was setup by default.
Follow my steps:
1) open VM Backend and click "Order status" link:
2) then click: "Confirmed".
Then change the "stock handling" field to "is removed"
Is Available means: nothing will be changed in stock numbers
Is Reserved means: the
Booked, ordered products number will increase so it become "reserved" for that buyer - to avoid any simultaneous purchasing- but the real stock number will remain the same.
Is Removed means: The Real Stock number will reduced.
finally the list should appear like this: