V1.5.3

Is this a bug or my misunderstanding of stock level functionality?

Check stock level = true
Subtract stock = true
Allow checkout = false

Product contains attributes that do not affect pricing.

Test #1
Total currently in stock = 11.8 total regardless of attribute selection.
Customer attempts to add 12.0 items to cart & receives the Yellow, not enough in stock, please adjust quantity error

Test #2, same product
Total currently in stock = 11.8 total regardless of attribute selection.
Customer adds 10 items, attribute small to cart. All OK
Customer adds 2 items, attribute large to cart. All OK
Customer checks out all ok
Store owner doesn't have enough stock to fill order because only 11.8 in stock.

Stock level after checkout = negative 0.2 items

My logic is that the second line item added to cart would have brought the total below that in stock and should have received a warning, since there would have only been 1.8 items available for sale after the first 10 were added to the cart.