Steps to Recreate;

(1) Set 'Debugging messages' to DEVELOPER.
(2) Upgrade from previous version of Moodle (in my case v2.6.1+ Build 20140123) to current release: v2-7-2+ Build 20141024.
(3) At each stage during the upgrade warnings are logged to the PHP log (Attached).
(4) Also, after upgrade has completed warnings are logged upon each execution of 'purge all caches' (Attached).

I'm currently testing and patching this local development version v2-7-2+ Build 20141024 prior to deployment and would like someone to verify that these warnings can be safely ignored. These warnings are not logged with the current version in production: v2.6.1+ Build 20140123.

Same behaviour when tested with version 2.7.2 (Build: 20140908) and version 2.7.2+ (Build: 20141028).