The Adept prodigy in 1.6 was known to give an additional 0.3 mastery in some cases, often when the player got an escort tree.
Now the effect of Adept has been changed, but this bug still remains and can be triggered, when you get bonus mastery over a tree whose category type you have a bonus mastery on, though these cases are much less likely to happen now. Currently there're 3 items giving bonus mastery to category types: Ring of the Warmaster giving bonus to Techniques, Rope Belt of Thaloren giving bonus to Wild-gifts if the wearer is a Thalore, and Radiance giving bonus to Celestials.
Examples of cases that can trigger this bug:
You don't have Conditioning tree and have saved a warrior escort with the Ring of the Warmaster on. Then you'll get the Conditioning tree at 1.60 mastery.
You, a Thaloren Oozemancer who already unlocked Fungus tree with a category point, went to Zigur to complete the antimagic trial and then killed the High Tempest and came back to Zigur again to claim the rewards, with Rope Belt of Thaloren on all the time, will have both Antimagic and Fungus trees at 1.80 mastery. You get the 0.20 bonus mastery to Wild-gifts twice when the quests increase the masteries of the 2 trees.
You can even unequip these items later, and the "free" bonus you get won't dissappear.
