Issue with MySQL trigger vs. Phalcon

Hi, I have a location table with columns lat, lng and the geohash of the point, and associated Location Phalcon model. In MySQL I have a before insert type trigger function that automatically generates the geohash (as a VARCHAR) when a location row is added, so if I put in the SQL:

INSERT INTO location (lat, lng) VALUES (100, 100); 

the geohash for (100,100) is duly inserted in into the geohash column.

However if I user phalcon like this ...

$location = new Location();
$location->lat = 100;
$location->lng = 100;
$location->save();

... the trigger is ignored (or perhaps the value it writes is overwritten) to NULL. Am I missing something? Has anyone else had simillar isses with MySQL triggers vs. Phalcon. Would like to know why this is happening. Any ideas much appreciated.