When giving yourself blocks like stone, you can get unexistant ID's, like for example /i stone:1000 1, however when trying to get Mobspawners or many other blocks, that were not updated with 1.8, you can't. This is not really a bug, but since plugins sometimes use the Data-Value to store information (like Essentials, to store what kind of mobspawner it will be converted to after placement), this should probably not be limited.
It breaks plugin functionality. It does not really make sense to have blocks with unlimited data-value, but for most it doesn't allow storing it.

This bug started existing with the 1.8 builds. Using /give player mobspawner:123 will just give you a mobspawner without the data value.