Products with Options not calculating stock correctly

Version 3.0.3.2
Example of problem: We have 1 pendant in stock, we have a choice of 4 different chain lengths ( 5 of each length in stock).
A customer adds the last pendant to the cart with one chain length no problems, but then is able to select the same pendant with a different chain length and add it to the cart with no out of stock warnings anywhere in the process of checking out and paying.
After OC recaculates stock levels it then does so correctly as -1 but too late to stop the oversell.

The product is set to reduce stock of itself and its options and cart set to not allow an out of stock product to be sold.

Regards
Tim