Mastery Levels lost after switching server

Hey, I just wanted to know if it's normal that you lose all ur mastery levels for champions when you switch to a different server? Cuz I changed server from euw to na yesterday and I'm a little sad about this :/ I know there was written that you lose ur ranked rank but I cant remember reading anything about losing mastery levels/xp...

Is this intended to be like this, or is it a bug?

-Yanni