Sorry for another post.

A few different things going on here. This is in response to Class B "output policy."

First of all, it's unclear to me which Class B transactions are valid because the mastercoin implementations do not follow the requirements of the specification. Second, it doesn't matter what the policy is regarding the validity of a Class B transaction, it's only necessary that implementations have consensus, and that consensus is modeled after the specification. Third, despite the overarching importance of that which is described in my previous point, policy regarding validity of Class B transactions should be specified in a manner which is beneficial to the user or minimizes the detrimental impact on the user.

Fourth, the flexibility of Class B transactions directly affects the ability to spend a P2SH output, and the likelihood that it will be spent. Fifth, policy regarding valid Class B transactions should be based on the balance struck between the Mastercoin Foundation's willingness to recognize transactions that are, or may be, directly detrimental to the blockchain, and whatever benefit is found in flexibility. Finally, however valid Class B transactions may be defined, a wallet should always create P2SH outputs that will be spent by the wallet from which it originated.

tl;dr Flexibility is okay. Wallets that create outputs that it cannot or will not spend are not okay.