I use Corona 1.7.
Just noticed an odd behavior.
When I work on a scene (around 6M poly) everything is smooth.
If I try to fire up IR - everything is okay.
But once I start the progressive rendering (with DR) it starts normally, but once I stop it and go back on working the scene everything is sluggish and laggy.
If I save and restart 3dsmax with the same scene - everything is smooth again.