PHP's is_subclass_of function causing failure in some contexts

I have a suspicion that this is related to issue: DC-386

The bug manifested its-self by bailing with no php error output when calling Doctrine_Pager::execute() in php 5.2.10 (5.3 appears to work - Mac OS X while 5.2.10 fail on ubuntu and centos).

I traced this down to Doctrine_Record::processPendingFields(), the offending line number is #477.

Interestingly, if I call is_subclass_of() with exactly the same params in my view just prior to calling Doctrine_Pager::execute() in my code, the error does not present its-self , i.e. I'b adding the following code :

is_subclass_of('Doctrine_Hydrator_RecordDriver', 'Doctrine_Hydrator_Graph');

It can also be avoided by calling Doctrine_Pager::getQuery()->getQuerySql(); and no doubt other code paths which change the environment in some way.