The 1.9-block "Path" (the block, when you right click grass with a shovel) gets destroyed even when you place a sign over it. The sign can be placed on top of the path or on a wall. This bug affects fences, too. (Every non-solid block).

And a second bug: You can't right-click dirt to create a Path. It only works on a grass-block. I don't know if this is wanted or a bug.