Another issue similar:
When I opened my GC account in 2008,
I guess I entered my weight in LB, while I was in Metric (208Kg ).
I changed the value in my profile, but this applies only for that date and so on.
Although I can enter manually weight to override the faulty entry,
as soon as I leave the health page an get back, the value recorded
directly from the garmin profile gets back.