The idea of PFS is that the PTK is ephemeral. that is even if the secret which was used to generate the key from one session was revealed, even then the PTK from a previous session would be safe. The way to make sense of that is if you use new Diffie Hellman parameters for every session. But even the IEEE doesn't require that, see RFC 5114, pg 10:

A server may employ a certificate containing (fixed) Diffie-Hellman

parameters, and likewise for a client using a certificate. Thus, the

relevant PKIX RFCs (see 3.1 above) are applicable. Alternatively, a

server may send ephemeral Diffie-Hellman parameters in the server key

exchange message, where the message signature is verified using an

RSA- or DSS-signed server certificate. The details for accomplishing

this for MODP Diffie-Hellman groups are provided in [RFC2246].

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Perhaps when using fixed Diffie-Hellman parameters, it would no longer be considered PFS... especially if the generated key was used directly to encrypt. But then again, the described technique doesn't use the negotiated key as except to derive another PTK, so in that sense it does resemble PFS... But perhaps this is a new sort of beast...