There is a big problem on select boxes on Mobile Safari. I can reproduce it on the iPhone and the iPad.
Grab an iPad and go to http://demo.myfoodpress.com/online-order-menu/ and try selecting a size for the Variable Menu Item. The pop up box shift all over the place. It even disappears on the site I am working on.
Here is a quick video I did to demonstrate: http://cl.ly/0I2y031t0p45
I also gave my staging site url in the private box for you to check out how the pop up shift up and down then disappear. Try one of the menu items and try selecting a size.
A fix please?