It's definitely ASW but I'd hesitate to call it a 'bug.' It's a limitation of the sophisticated algorithms that do the spatial and temporal frame interpolation. It usually only shows up on fast movement of narrowly spaced patterns. There is a new v2 implementation of ASW on the horizon which can also incorporate z buffer data to hopefully eliminate these artifacts.
To answer the OP's question, what this really means is that for some reason your performance has decreased, and you aren't maintaining 90fps anymore. Thus ASW activates to keep a smooth framerate in your display. It could be an issue with your PC unrelated to FS2, or you might need to dial back your graphics settings in FS2. You can also force ASW to be disabled but you will then have a mediocre frame rate in your Rift rather than correcting the real issue.