Update April 14, 04:15 CEST
Yesterday, we implemented the hotfixes described above to support core gameplay in instances in Burning Crusade Classic Anniversary. Unfortunately, these changes were impaired by bugs that did not appear in our pre-release testing. The result was unintended behavior of drops for both solo and group players. For example: one bug resulted in some players becoming completely disallowed from rolling on loot.
With an update we sent to the live game a few minutes ago, we have reverted the original changes while we investigate these bugs.
Thank you for your feedback.