by dan attwood.
I've been working with Martin on this as we were seeing the same problem.
This is moodle 2.7 on ubuntu 14.04.
I've just applied your fix and it seems to be working fine now.
Has there been a tracker issue raised for this?
As this is a fix that requires a fix to core code I think someone at Moodle HQ needs to be aware of this and review it for inclusion into Moodle.
If you post a link to the tracker issue here we'll add our comments to it.