I saw this video of a quick tip on STM lenses and focusing. This issue must confuse lots of people, and even the presenter says "Review this before contacting support" so I thought I'd share here.
The author states "When manually focusing with STM lenses, an electronically powered manual focus system turns on, which may cause users to think something may be wrong with the camera when there isn't. Find out which steps you have to take before you start photographing."
I'm glad I saw that since I now have some STM lenses and I thought that going into MF mode & turning the focus ring is all that is necessary. Not quite true, as the camera can't be sleeping.