And it's a good amount too! Currently at level 101 they give the same amount as a quest. (15,200xp)
I noticed this while questing and it seems like it was literally JUST hotfixed as 10 minutes ago they didn't give experience.
Edit: Seems to no longer give experience, so was possibly implemented in error and then quickly removed... I have a screenshot to prove I got experience from multiple treasures but cannot post them for some reason.