One of my players said that when they buy something from the shop, it disappears from their inventory.  As admin, I'm not having any issues.  Their group has the permission to use the shop.
Any idea of the cause?

This is the first report of this bug that I have heard of... Nothing in the code would cause this to happen either from what I can see anyway. Are there any errors or anything in the console or rcon? 

Found the issue.  It didn't have anything to do with this plugin.
Thanks for the response though!