Throughout the history of this plugin the shopping cart has not been distinct between your shops - ie you could put some items in your cart in shop 1, logout, login to shop 2 and they'll still be there.

The original author saw this as a positive and even created the 'site links' to promote your shops to each other.

However this might not suit everyone - for example you might have a business model where each shop represents a geographical region and items are hand delivered - and the product range and pricing may vary.

From personal experience I've had users exploit this loophole to gain a cheaper price or attempt to buy a product that isn't actually available.

So v1.3.1 now offers the option to make the shopping cart distinct to each of your shops

This is the only change since 1.3 - so don't bother installing if you have it running and don't require this feature.

https://www.zen-cart.com/downloads.php?do=file&id=378