Although APC was not enabled (no apc.enabled = 1) in the bitnami install the module was enabled in php.ini (extension = apc.so). I had missed this. Apparently this was enough to cause a problem in PHP 5.4.37. I read that there was a bug in PHP 5.3 where people experienced similar issues with APC and class declarations nested in if() statements. Oddly I didn't find any reference to this with PHP 5.4. Either I missed it or there is something strange going on with the bitnami install of PHP in their Wordpress images. In any case, removing the reference to extension = apc.so from php.ini and doing a restart of both php-fpm and apache solved the issue with Tubepress. Unfortunately this really isn't the best solution as it would seem that I can't use APC at all.
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