This seems to be a bug within egroupware. It was identified in 1.8.004 but still not fixed in 1.8.006 
http://www.egroupware.org/forum#nabble-td3905452
Our server indeed runs on an alternate port. Here’s what I did to fix as per the recommendations on the post. I edited redirect.php as follows:
After the following line:
$path = preg_replace(’//[^/]*$/’,’’,$_SERVER[‘PHP_SELF’]) . ‘/’;
I inserted the following line:
$port = ($_SERVER[‘SERVER_PORT’]!=“80” || $_SERVER[‘SERVER_PORT’]!=“443”)?’:’.$_SERVER[‘SERVER_PORT’]:’’;
Next after the following line:
array_push($valid_referer, $path);
I removed the following lines:
array_push($valid_referer, ($_SERVER[‘HTTPS’] ? ‘https://’ : ‘http://’) . $_SERVER[‘SERVER_ADDR’] . $path);
array_push($valid_referer, ($_SERVER[‘HTTPS’] ? ‘https://’ : ‘http://’) . $_SERVER[‘SERVER_NAME’] . $path);
and replaced them with the following lines:
array_push($valid_referer, ($_SERVER[‘HTTPS’] ? ‘https://’ : ‘http://’) . $_SERVER[‘SERVER_ADDR’] . $port.$path);
array_push($valid_referer, ($_SERVER[‘HTTPS’] ? ‘https://’ : ‘http://’) . $_SERVER[‘SERVER_NAME’] . $port.$path);
Saved and it now works.