[SAI_Peregrinus]

Cryptographers tend to study things they think journals will find interesting. Attacking a theoretical construction that uses a known-vulnerable sub-method is unlikely to get grant money. After all, who would even make such a silly thing? So no one has attacked it that I've seen in the e-prints, though I haven't searched and am going from memory.

Then someone notices that the naivé attack doesn't work in one case. Sure, that case doesn't claim security against the attack, but they go ahead anyway.

Now it might be worth attacking. Especially if this gets used anywhere.

Absence of attacks is not evidence of security. Absence of attacks against non-weakened versions with attacks against weakened versions and plenty of margin is. EG reduced-round block ciphers.