Same exact problem I had with mine (hence the $200 deal). Turns out the filter was getting soaked with oil from the breather hose in the airbox due to a bad reed valve in the breather "block" itself. The filter was brand new, but it had become soaked with oil from the extra blowby getting by the bad reed valve.
Currently I rigged a hose to vent the breather outside of the airbox and have had no problems since while waiting for a new breather assembly.
Not sure if it's the same as your problem, but has the same symptoms (runs rich with aircleaner installed, runs fine without).
Best of luck.