Update Cart redirects to non-secure page

[Guest]

My customer base is not particularly Net savvy and I just noticed something (maybe saw it long ago but dropped it as a minor issue) that may be another cause of Cart Abandonment. When a customer initiates checkout, they are in HTTPS mode. If they decide they're spending too much and go back to the cart to drop an item, they are warned about unencrypted information since the cart updates values but returns to HTTP mode.

Is this normal osC behavior or something I did by adding a Contrib? (I have several dozen running).

Where do I change the behavior to have update cart stay in HTTPS?

Thanks for your help!