Affects Version/s: Minecraft 1.4.2
Fix Version/s: Snapshot 13w10a
Environment:Windows 7, Java 7 update 7
Grass blocks turn into dirt blocks after a while under upside-down stairs. The only exception is the oak wood ones (grass stays grass under them).
As you can see on the following screenshot it's pretty ugly.
Just place upside-down stairs on grass and wait.
How I think it should be:
Grass should not fade under any type of upside-down stairs.