I have just come accross a bug with this and i don't know how hard it is to fix.

This method (Max Quanitity =1) works when the user is already logged in and within the same session. For example, if the cart has 'product A' and user tries to add that product again, the action is prevented and the following error message appears:
"The quantity added to your cart has been adjusted because of a restriction on maximum you are allowed. See this item: product A"

However, if the 'product A' was added to the cart in a previous session, the store allows the user to add a second (or third or fourth, etc...) product A even when the max quantitiy value is set to 1. For example the user is logged out but their account already holds 'product a' in their shopping cart. The user adds another 'product a' while in the visitor's cart and seeks to checkout. They are then prompted with a login request and when complete they now have 2 of 'product a' with the following message:
"NOTICE: For your convenience, your current shopping cart has been combined with your shopping cart from your last visit. Please review your shopping cart before checking out."

1. How hard is it to fix this bug? So that the store check's whether product max quantity is reached before merging the visitor cart and the user cart?

Thanks in advance,
Shaztesting