Hi
I have exactly the same problem.
My SIM is a French SIM. I work in Belgium. Whilst in Belgium, the roaming triangle appears.
When I go back to France, the roaming triangle still appears intermittently. This is worrying. I'm not sure how I'm billed.
How does my operator bill me? Does the operator receive an incorrect LAC or RAC?? even whilst in France?
If my mobile phone is sending (whilst in my H.PLMN) a foreign LAC/RAC combination or TAC code (4G), then I'm so screwed.
Microsoft should be paying me for the data usage. I'm really upset. I hate the fact that I've spent all my life debugging Microsoft products. I should have stuck with Apple, but they were too expensive.