Shipping Address not editable (inputs disabled)

For some reason I cannot modify my shipping address, both in the Profile Details page and the Checkout page. Checking/unchecking the “Use my billing address” option does add and remove a “disabled” class from the elements, but it does not remove the disabled attribute.

Any ideas why this might be happening?

Im using version 2.2.4, with a custom template based on Austere. Other than CSS, I have not modified the template files for either of these forms.