I have 1+, also with SMARTONE and I go on business travels every month (5-6) days only but I havent had such a data leak charge on my bill (I just checked online).
HC what $$$ package are you using per month, I have the rip off price one at $345 per month Not sure if that makes any difference.
If you really want to do an experiment is go to top of tai mo sha where local networks are crap and watch your phone suddenly change to roaming in China, turn phone on and off a few times, go home and see if any roaming data was marked