I also thought that it is an ICAO official change from saying "mb" to "hpa" ?? I have certainly applied this for the last couple of years...
Ahhh our good old friends ... " I am flying , not sailing, in International waters ****** Controlled airspace...we do our own thing " American friends .... because although we live and closely share one world we cannot comprimise on measurement standards ...yea I have personally had it, on two occasions, when the QNH has gone to below 1000 hpa that a dear American pilot would take that as inches ...ie 997 hpa is 39.97 inches ...
Ps There was some valid reason why "mb" was replaced with "hpa" ..just can't remember oof hand what it is ...