I have a world with a store based on the XP level, I have this world since the commands came to MCPE and it has always worked.
When I downloaded the beta I discovered that the command that takes the xp from the players doesn't work.
I tried with lowercase "l" and uppercase "L"
I always use "/xp -10(or any other amount)L @p" and well... it doesn't work.

I tried with giving xp and it doesn't work neither.