I have heard of it before.
The PCM uses the rough road information to enable or disable the misfire diagnostic. The misfire diagnostic can be greatly affected by crankshaft speed variations caused by driving on rough road surfaces.
I believe it has something to do with the vehcile speed sensors as well. If one wheel suddenly spins faster while the other three are moving at another speed, the PCM says hey, something is wrong here.
I suppose it was like when I had my Vette on the dyno and only the two rear wheels were moving, it set codes.
