Stock not counting down

On my new webshop I sold two items – in both cases the stock-counter did not change.

Since I sell single artworks, it’s pretty important that I don’t double-sell. ( http://www.oxpal.com/shop )
Both these were paid via paypal, maybe that’s the issue? An earlier sell went fine.
I did get confirmation emails for the sale. Though the second took soo long that already before I’ve changed the item’s status. But I assume status should change instantly- there wouldn’t be a delay, right?

There is a user with the same problem it seems (just his post is not here in the WooCommerce section, so I guess the support won’t see it: http://wordpress.org/support/topic/woocommerce-stock-problems )

(Current version of WooCommerce and WordPress. Personal theme. For each item I check “Enable stock management at product level” and “Enable this to only allow one of this item to be bought in a single order” – and set the quantity to 1)

http://wordpress.org/extend/plugins/woocommerce/