A well-known XPlane developer and also Austin himself claim Austin received an email from an informer with inside knowledge that Asobo developers are secretly, and possibly illegally, using XPlane as a base to develop MSFS’s FM:
It sounds quite paranoid, but I think Asobo and their collaborators should at least know what insinuations are being leveled at them by other sim developers.
@staff
Please close this garbage, keep the toxic avsim ■■■■ on avsim.
This place is too clean and too much of a breath of fresh air as an environment for such lowly sources and drama. Don’t spread the toxic avsim forum drama pandemic here, let people find that dump of a thread on their own.
When the sim was first released, it still had the “license” jpegs from the FSX flight training system. I highly doubt that the so-called informant is being truthful. What I find more likely is a disgruntled user that didn’t get exactly what they wanted right out of the box (so to speak), and decided to cause trouble for Asobo.
What’s FM stand for?
Flight Model
I’m almost certain it’s somebody disgruntled, and if it was just users flaming Asobo it wouldn’t be special. But this is Austin himself and a major Xplane 3PD joining / promoting the speculation. That suggests they believe the claims have some merit, or should at least be considered / looked at.
Shouldn’t it read Xplane plagiarizing Asobos lighting model? 
For real. I’ve said this before but Avsim always has been and always will be, the “hardcore” simmers who will take one blog post and talk about it for 50 pages worth of forum posts like it’s the discussion about the impending apocalypse. People are weird sometimes
Huh? The flight model in this sim is not even identical to X-PLANE. Stay clear from Avsim and oh the X-PLANE forums!
I guess if there is anything to it then I suspect that would be a matter for the respective legal departments.