Readonly attribute handled differently in IE7 and FF

Readonly attribute handled differently in IE7 and FF


Using jQuery 1.3.1, the following line works in IE8 and FF.
$("input[name$='DateString']:not([readonly='readonly']),input[name
$='DateString']:not([readonly='true'])").datepicker
( dpOptions ).addClass( "date" ).attr( "maxlength", "12" );
But does not in IE7. I had to alter it to
$("input[name$='DateString']:not([readonly='true'])").datepicker
( dpOptions ).addClass( "date" ).attr( "maxlength", "12" );
Because I have to support IE7, my workaround is to break it out
$("input[name$='DateString']").each( function(i) {
    $(this).addClass( "date" ).attr( "maxlength", "12" );
    var ls_val = $(this).attr("readonly");
    if ( ls_val == false ) {
        $(this).datepicker( dpOptions );
    }
});
which works well enough, just not as appealing.
This appears to be a bug in jQuery. Any thoughts?
David