The word from HTC
Yup, looks like the Lockscreen was not the answer.
Neither is the HTC Framework update that appeared yesterday. Oh well.
Contacted HTC Australia, they are aware of the bug, and their official advice is as per the previous post recommendation: disable Google Play Services & Google Services Framework.
Not a nice solution, as it will kill a lot of your GApps, but that's all we can do right now.
So:
Settings
Apps
Scroll right to All
Scroll down to Google Play Services
Tap Disable
Repeat for Google Services Framework.
I guess you can selectively re-activate these apps if you need the Play Store or other GApp service.