I don't think this is anything new. There are miners out there that allow any valid transaction and don't perform an isStandard check at all. This is why the process for upgrading is to first get a pledge of support from a supermajority of the mining power and once that's achieved, set a date in the future to start the full validation of BIP16 transactions. Miners will have a couple weeks to upgrade and avoid mining potentially invalid blocks.
As far as I know it's basically only luke-jr that doesn't check IsStandard, and even he's been known to forget to disable it on occasion.
There is no reason to expect BIP 17 will have any such problems.
BIP 17 might be even worse actually. Obviously, correct attempts to spend BIP 17 transactions won't be included in blocks by miners like this because the spends won't pass IsStandard, but I think it should be possible to create transactions spending them that are invalid according to BIP 17 but treated as both valid and standard by non-BIP 17 miners.