Already reported to bug tracker, but hoping a few people can test this to verify...
Enable Inventory Tracking = YES (checked)
Allow Negative Amount in Inventory = NO (not checked)
Product has no options
Product Inventory is set to "Track without options"
Create (use) an order (call it order #99) with the sale of (1) "widget".
Set inventory "Qty" of the widget to "0" so the widget is now "out of stock" and save.
Click on Order # 99 so show the order detail. Select "edit order" and change the quantity in the order from (1) to (2) then hit save. It will display 2 warnings and then saved ok.
WarningThe number of products in the inventory is not enough for your order
WarningLow inventory of "Widget #XXX"
Congratulations!Order has been saved successfully.
Check the inventory of "widget". It will now be (1) instead of (0) or (-1)
This is a big problem for anyone who edits orders as it creates phantom inventory.
Please let me know if you see the same behavior. Thank you.