Affects Version/s: Minecraft 16w39c
Fix Version/s: None
It seems that when you use /fill with a blockstate rather than a data value, it will only apply the blockstate to the filled blocks with the lowest X coordinate. All others will be filled with their default blockstate. Using data values instead of blockstates works as expected.
To reproduce: simply run the command /fill ~ ~ ~ ~2 ~ ~2 minecraft:dropper facing=west
All the blocks with the smallest X coordinates will properly face west, while the others will all face east instead.
EDIT Some more testing shows if you try it with facing=north, the blocks with the lowest Z coordinate will be facing north while the rest will face south. So perhaps this is an issue specifically with orientable blocks rather than blockstates in general?