I was able to pick up the [item]70142[/item] today, and I began doing some tests with a fellow balance druid friend. I realized that either my thinking of how Mastery works has always been WAY off base, or they’ve changed how Mastery affects Eclipse since the start of 4.0. If I’m way off base, I’m not the only one, because I know other balance druids who shared the same thought.
The tooltip for Eclipse is misleading. The damage reflected by the tooltip is based on the mastery value when you actually proc the Eclipse buff. I had mistakenly understood that your Eclipse actually maintains this value of damage, even if additional mastery falls off. (Such as which is provided by the Chalice or [item]65105[/item].). This is not the case. The damage you do under Eclipse is reflected by the amount of mastery you currently have. If mastery falls, your Eclipse damage will fall as well (although the tooltip will not reflect such). If you gain mastery after proc’ing Eclipse, your Eclipse damage also increases, without a change to the tooltip.
This is going to cause me to re-think how I value mastery. I realize I’m probably a giant tool for not understanding this a lot sooner, but I know I’m not the only one.