I’ve identified the cause of the problem & understand what’s been going on. It is timing dependent, so it won’t consistently reproduce, hence why I haven’t seen it in the editor and why our QA didn’t spot it sooner. Fixing it will take a little longer & I’ve no idea which release the fix would end up being part of.
Future releases will be tested against Yosemite so that we are ready for it when it arrives, but we have to pick our battles until then.