It seems like the difficulty threshold on suprnova being as low as it is is tripping their share spoofing detector or something... I only get about a minute and a half where the miner shares are accepted (both with djm's miner and nvMiner-D7), and then every share is rejected.

Edit: Seems the suprnova guys are onto the issue! https://bitcointalk.org/index.php?topic=713003.msg8089093#msg8089093

Edit2: Seems they overshot on the difficulty... A bit too high for my rig at least.