The storage field must be included in the reconfigure update in addition to changing the disk size.
When submitting a storage reconfigure request through the API exposed by /catalog-service/api/consumer/resources/{{ResourceID}}/actions/{{ReconfigureActionID}}/requests, API users need to modify both the 'size' property of the disk to be resized, as well as update the value of 'storage' to reflect the new sum of storage consumed by the machine (after the resize).