watch -c --differences=permanent misbehaves (highlights everything)

If the watch -c and --differences=permanent options are combined, then upon the first update _every_ character is highlighted even if nothing has ever changed.

It appears that -c ("Interpret ANSI color and style sequences") tickles a bug in the persistence logic. Regular non-permanent highlighting (with option -d) works okay with -c.

STEPS TO REPRODUCE:

1. /usr/bin/watch -c --differences=permanent -n 1 echo This never changes

RESULTS: After one second all output is highlighted

EXPECTED RESULTS: No highlighting until something changes

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: procps 2:3.3.10-4ubuntu2.3
ProcVersionSignature: Ubuntu 4.4.0-62.83-generic 4.4.40
Uname: Linux 4.4.0-62-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Jan 22 17:35:09 2017
InstallationDate: Installed on 2013-08-06 (1266 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
SourcePackage: procps
UpgradeStatus: Upgraded to xenial on 2016-05-11 (257 days ago)