MarketPress not working correctly

I am using the paid version of MarketPress. I am having an issue which prevents me from adding a quantity when entering inventory.

The quantity field is set to "0" by default. When I check the "quantity" box, and try to change the "0" to another value, it won't allow me to enter a number. It is stuck on zero.

I had spoken to someone at the live support department, and he instructed me to disable all of the plugins so that I could see if one of them was causing a conflict.

I did, in fact narrow the problem down to a plugin called the "Elegant Builder", which was created by a company called "Elegant Themes".

I need that plugin, so removing it is not an option. I was instructed by the live support rep to open a support ticket here on your website.

Any help in resolving this issue will be much appreciated.

The website which I'm refering to is:

Thank you very much for your time and support!

From Andrew Glover