[CentOS] Emacs issue in CentOS 7

Sometimes when I save a file in emacs, it thinks that the buffer is
still dirty. If I use C-x C-w to write the file, I get an overwrite
warning but the buffer always goes clean.

Perhaps this is related to the file atime? My /home is btrfs with
relatime. I always thought emacs was smarter than that, for example
I run emacs on files mounted noatime on CentOS 6 without any issues.

A bit of searching the interwebs did not provide any clues. Anyone?

-- greg