On my test machine (a Windows 98 box running the precompiled Win32 PHP 4.0.3pl1 binary as a CGI program on top of Apache 1.3.12), the following (admittedly bizarre) code will crash PHP:

$db = odbc_connect("db1","","");
$result = odbc_exec("SELECT * FROM table1");
while ($odbc_fetch_row($result)) {
  print odbc_result($result, $result);
}

It will crash it no matter what resource ID PHP has assigned to $result, and even if odbc_result's arguments 1 and 2 point to different result sets, even from different databases.