experience points can get stuck in hoppers.

What I expected to happen was...:
We made a mob grinder in a previous version, with hoppers at the bottom to collect the drops. When we killed the mobs then, the XP points would float to us. 

What actually happened was...:
In the newest update/snapshot some of the XP points get stuck in the hopper, sitting in the small dip of the block.

Steps to Reproduce:
1. put hoppers at the bottom of a spawner.
2. have the hoppers going into barrels.
3. have a block above you, thus allowing for visual into the spawner at only your eye level. 

4. mobs should drop to where you can see their feet only, the should be standing on hoppers that are at your feet level. 

5. upon killing the mobs, some of the XP may get trapped in the hopper block. This does not happen every time