I think that's probably it. D47 gets nasty quickly above 20c but I've had no problems since controlling the temp and it packs tighter than anything else I have used which is good for reducing racking losses.
Huh.... mine too and all my batches that used d47 just weren't very good. I figured it was mainly the temperature variances between night and day. The same exact recipe brewed at the same time with 71b was great.
"Gaurd your honor, let your reputation fall where it will, and out live the bastards."