I just completed the Mauve Manticore #2 Supplement for the first time and earned a gold chest. It contained: Inspiring Chain Shirt (common) Copper Spear (uncommon) Stormstaff (uncommon) Sword Of The Lion (uncommon) (Shiny Adventurine) (uncommon) The description of the Magnificent Chest (gold) in Chest and Barrel says "1 rare or better". Maybe the magnificent chests you buy are different from the gold chests you get from completing a module for the first time, but I was surprised to get only commons and uncommons. I'm playing on the live server, which I believe is running version 2.65.2. (I'm not trying to be greedy here, and I apologize if I'm just confused about how chests are supposed to work. But if there's genuinely a bug in the loot awards, I figured you guys would want to know about it.)
The rewards I described above were from the very first time I completed the module. So either the Mauve Manticore modules (or just the supplements?) don't count as "adventures" for this purpose, or I wasn't huffing paint after all.
Another data point: Completing MM5 for the first time on the test server, I got UUUR(U). So while I did get a Rare, the club reward was Uncommon so it wasn't a guaranteed Rare. And I didn't get a single treasure form that module.
Bump. This is still happening, and happens even in non-MM adventures. For example, alternate account completing these adventures for the first time: Garnet: CCUUtUt(U) Tvericus: CUUtUt(U) Citrine: CCUU(R)
Not a bug. First time completion reward enhancement as mentioned in that blog post was canceled at some point. Confirmed with Jon a few weeks ago, sorry I didn't post here.
Not that I would have minded the free rares, in my first playthrough. Well, in the case of the Manticores, they really need all the encouragement-to-play they can get, so a guaranteed chest at the end isn't a bad idea, at least for them.