If you place a piston down then grass then redstone block, it will power the piston once grass is destroyed.
Seems to only work with piston(tested with sticky).
It appears to be related to block update, if you leave grass (2) and let it turn to dirt, then it will activate piston.
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40th duplicate of MC-108 , please use the search function to see if your bug has already been submitted. Currently over 42% of tickets are being closed as duplicate.

Just looked at MC-108, and while its similar it doesn't mention the fact of block update being an issue. And this method does not require a second redstone source. Last time I'll submit a bug for mojang, sorry your over worked looking at pictures of redstone and bugs.