Not a 3.06a issue, just started this afternoon (3/30). May be a change in the lookup query at discogs.com (which still shows covers in its internal queries).
They're currently playing with their image URLs, which disturbs the image caching proxy I'm using. I've already adapted the proxy to deal with most changes, but it seems not all.
I've made some adjustments here and it should be working again.
Yes. Back again. Thanks.