TripodException failing to report underlying error

[kiyanwang]

Last week I was debugging a migration script on one of the tarl jobs boxes. The script was dying without reporting any errors. I worked out that it was failling when making a call to tripod but couldnt understand why a Fatal error wasnt being reported so I added a Try catch around the call to a tripod method i.e.

try {
  ...
} catch (Exception $e) {
   echo $e->getMessage();
   echo $e->getTraceAsString();
}

The exception was caught but I got an error stating that $e has no method getMessage() or getTraceAsString(). On the other hand if I simply called

var_dump($e);

It confirmed that $e was a TripodException and within its properties I was able to figure out why my code had been failing (unable to connnect to MongoLab due to firewall restrictions) but what worried me was why the standard methods on Exception were not available when TripodException is defined as:

<?php
  class TripodException extends Exception {}

Btw I did try catching it as a TripodException and the results were the same.