For some reason known only to Finagle, God of standard violations, some X11 configuration files use a ! to delimit a comment. This is not recognised by dispatch-conf, so trivial changes in these files have to be hand-cranked. An example file showing the problem is /etc/X11/app-defaults/XFontSel
Steps to Reproduce:
There are some config files where "!" is meaningful.
The real solution is to revise the way x.org handles comments. I'll propose it to them.