TCP TSecr question

Hello,

There is an issue with this field in SYN packets when tw reuse/recycle is on. Quoting from RFC 1323, section 3.2:
The Timestamp Echo Reply field (TSecr) is only valid if the ACK bit is set in the TCP header; if it is valid, it echos a times- tamp value that was sent by the remote TCP in the TSval field of a Timestamps option. When TSecr is not valid, its value must be zero. The TSecr value will generally be from the most recent Timestamp option that was received; however, there are exceptions that are explained below.

On Linux, when the sysctl_tcp_tw_reuse or recycle is on, the most recent timestamp from a previous connection is sent instead of 0. From what I've seen in the source, this has to do with PAWS against delayed/duplicate SYN packets.

My questions:
1) Is this violation of RFC 1323 useful in PAWS or did I misunderstand the whole situation?
2) Is there any other RFC that amends 1323 to specify this behavior or is it a Linux-specific enhancement?

Thank you,
Cosmin.