Exp changes into Exp Bottles

I found the bug through a mistake.
There was a Mob Spawner and i wanted to block it´s spawn.
Unfortunately i missclicked and build a wood block on the side of the Spawner.
In this Moment my exp ( lvl 21 ) turned into dropped exp bottles. I collected them and got a different amount of exp.
i tested it later on my own server and it worked again.