Man Flex
you are totally correct. "report your heading" has no implications meaning you must stay on it... its a fairly wishy washy phrase, but I might use it if I want to guage what I think is a good track for future A/C that I MAY wish to put on similar tracks; on headings, wether that be traffic reasons or positioning for next sector.
If I wanted you to report and stay on a heading I personally would use "continue present headin and report it"