Can you break this down for me? I don't get it. I thought the rested exp is always "+ x%" for a length of time dependent on how long you were in the area. What exactly does resting on a level 50 do for a level 1 when you switch?
Rested XP accumulates as x% of a level.
Your rested XP value is tied to your character data and not your class data. This means that you have only one rested value for all classes, and all classes will accumulate or diminish that rested value.
So if I spend enough time resting (moon icon under xp bar) to accumulate 50% of a level, then my rested value is 50%. It doesn't matter what class I did that on, and they all accumulate at the same speed (because it's not a fixed amount of xp, it's a percentage).
What I cannot yet confirm (others may) is whether rested xp accumulates if you're resting on a level 50 class.
Detailed breakdown of the process:
Let's use a level 40 PGL and a level 1 MRD, both on the same character.
PGL40 rests for 50% of his level. His rested bar now extends past his gained xp for 50% of the value of that level.
So let's say he needs 200,000 xp to level and has 12,000 of it right now. His rested value (50% of his level currently) extends for the next 100,000 xp on PGL. Rested xp is consumed when crafting, gathering, or killing monsters. It is not consumed by turning in quests, completing hunting logs, uncovering map areas, or any other source of bonus xp (like finishing a dungeon with someone new).
So we have our guy here with his 100,000 potential rested xp. He's sitting pretty, but he's also a little bored of PGL at the moment. He wants to start MRD. So he puts on his axe, and bam he's a MRD.
His MRD now has 50% of its level as rested xp.
So let's say MRD at level 1 needs 500 xp to level. 250 xp is now rested and will be consumed by the things I mentioned above.
He burns that in 16 minutes, because level 1.. and switches back to PGL. His PGL now has 0% rested xp.