Ned -
For the record, I've had that happening too intermittently on a debian server. I have never been able to nail it down (or reproduce it consistently), but it looked like some previous UUID generator was locking up /dev/urandom. Simple 'cat'-ing /dev/urandom used to cure the situation, as did an ugly variety of workarounds...
I believe that what was happening may have been that the UTF-8 text converter attached to the stream may have been trying to interpret the bytes.
This might well fix the bug that started this thread, but if so, mine was different. The UUID generator bug I am describing has been happening for the last couple of years, well before the UTF stuff. The scenario was always that all 4 bytes read from /dev/urandom appeared as nil, which caused a walkback. (As I said, cat/more/etc. on /dev/urandom unblocked it).
The issue is moot however: since I the server has migrated, I haven't seen it happen (but I haven't had a rush of UUID creation either).
Michal