Using the following function as the error handler, the errormsg always ends up blank, though all other fields get filled out as one would expect.

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script which reproduces problem
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function customErrorHandler ($errno, $errmsg, $filename, $linenum, $vars)
{
    $dt = date("d-m-Y H:i:s (T)");

    // What kind of errors can we get?
    // we probably only care about (user)error, (user)warning, (user)notice
    $errortype = array (
        1   =>  "Error",
        2   =>  "Warning",
        4   =>  "Parsing Error",
        8   =>  "Notice",
        16  =>  "Core Error",
        32  =>  "Core Warning",
        64  =>  "Compile Error",
        128 =>  "Compile Warning",
        256 =>  "User Error",
        512 =>  "User Warning",
        1024=>  "User Notice"
    );

    // set of errors for which a var trace will be saved
    $user_errors = array(E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE);

    $err = "<errorentry>\n";
    $err .= "\t<datetime>" . $dt . "</datetime>\n";
    $err .= "\t<errornum>" . $errno . "</errornum>\n";
    $err .= "\t<errortype>" . $errortype[$errno] . "</errortype>\n";
    $err .= "\t<errormsg>" . $errmsg . "</errormsg>\n";
    $err .= "\t<scriptname>" . $filename . "</scriptname>\n";
    $err .= "\t<scriptlinenum>".$linenum."</scriptlinenum>\n";

    if (in_array($errno, $user_errors))
        $err .= "<vartrace>\t".wddx_serialize_value($vars,"Variables")."</vartrace>\n";

    $err .= "</errorentry>\n\n";

    error_log($err, 3, "/var/log/php-error.log");
}

$old_error_handler = set_error_handler("customErrorHandler");

-----------------
configure command
-----------------
'./configure' '--with-imap' '--with-pgsql' '--with-gettext' '--enable-snmp'
                                         '--enable-track-vars' '--enable-wddx' '--with-gd=/usr/local' '--enable-trans-sid'
                                         '--disable-magic-quotes' '--enable-short-tags' '--with-apxs=/usr/local/sbin/apxs'
                                         '--without-mysql' '--without-tsrm-pthreads' '--prefix=/suproot/usr/local'