You can't push a daylight sensor with a piston, while there's no reason for this not to be possible.
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kumasasa
migrated
If the comparator is not pushable, how does it drop a repeater? it doesnt for me.
kumasasa
Proably this is by design, because Daylight detectors have a Tile Entity (see http://www.minecraftwiki.net/wiki/Chunk_format#Tile_Entity_Format) and blocks with a tile entity are not pushable.
migrated
Reason found.
Confirmed.