3ds Max :: DBR Gets Slow

I never noticed this in previous versions, but over time while working in a Max session DBR seems to get progressively slower until it becomes a real drag. To the point that a frame that takes only 10 secs to render locally starts taking about 2 mins with DBR. Re-start Max and load the scene and it's back to normal. Or something that can be purged to clear whatever causes this lag without re-starting?I don't use DBR for final production renders, that's done with Backburner. But I find DBR useful for fast test renders while working on materials and lighting, to get a look at how it's looking. So I do a lot of single frames while working on a scene, that's when I get this slowdown.