Script:
<?
$r='nan';
$s='nan';
if ($r != $s)
    echo "This is weird!";
?>

./configure --enable-track-vars --disable-debug --with-pgsql

I don't use a php.ini file

This problem is not confined to this release level.  After discovering this problem I tried it on your other two betas and the last release before that with the same result.  Any other string seems to work, just not 'nan'.  The problem does not exist on another computer running the same php and postgres but using linux 2.0.36.  The problem occurs in the apache module and the cgi.  I have checked that the strlen of both is 3, I have compared each byte like $r[0]==$s[0] and that works, but comparing the two strings always fails!  The computer is a Dell Poweredge 2300 with a 500 mhz Pentium II processor.