viewtopic.php?f=23&t=1251
In this patch, when enhance gems were added over 8 months ago, It states that they "Can be found in chests dropped from visits/battles/bosses (6% of chests)."
After looking through all other patches, it was never removed that they wouldn't drop from bosses chests, BUT, They never have dropped from bosses chests. After over 1k raid boss wins, this is a bit of a piss off.