I think it is reportable – http://new.hbinfo.org/legislation/main-regulations/regulations/regulation-88-duty-notify-changes-circumstances – para (3) gives the list of things that are not reportable. All changes that might affect entitlement need to be reported and I would say this comes within that general duty. A change in tax paid is likely to change net earnings.
You can then go on to look at whether the entitlement is affected and make a decision.
