Hi
It has nothing to do with my changes. It's a bug from VM where cart cannot work on a pages not connected with VM component, simply becuase it's missing files component is loading (my guess at least).
There is an easy test to try, move cart module to a one of module positions available on Protostar, default joomla template, for example "debug" and than switch to a Protostar template. You will see even without using our templates problem still exists. I'm guessing connecting via AJAX as done previously was keeping cart away from this problem.
As a solution I would propose to connect homepage with VM, but I think it would be best if You would ask VM support about a fix to this.