Website jumps when tab is pressed while filling out form using Chrome

I am building a simple website where users can buy/order cookies... The site is very much in the development stage, but I have finished the order form. However, for some reason, when users are filling out the order form, the site sometimes jumps up and down the page when using tab and shift tab to navigate the inputs.

It doesn't always happen, but usually at least once while filling out the form. Just keep pressing tab and shift tab and it will happen. It seems to happen more frequently when you tab through the form after text has been inputted in each field.

To see and test the form, click here to go to my page, and then click "Delivery Information".

From my own testing, I can only duplicate this error with Chrome and have not been able to with IE or firefox.

Any ideas as to how to fix this?

Thanks!