Ok I narrowed down the Particles BUG.
This happens only in iOS Tier2.
I start my game as landscape:
agk::SetVirtualResolution (960, 640);
agk::SetResolutionMode (1);
agk::SetOrientationAllowed (0, 0, 1, 0);
This causes particles to come out rotated 90degrees upside down! I tried using various particle images for testing, and the bug is constant.
If I start my game in portrait particles are drawn fine. But as I rotate horizontally they are rotated 90degrees upside down!
Please use irregular shaped particles when testing, as the ones in the samples are symmetrical shaped and the bug won't show.