This is a rather strange fontification error. Sometimes lines after a
certain line or the last part of the line itself gets fontified as
strings (which is incorrect) and sometimes not. I do not believe I am
able to make a simple example of this. Instead I have put up a copy of
the file where I saw it on the web:
http://ourcomments.org/Emacs/DL/html-syntactic-err-l164.html
To reproduce the error download this file, start Emacs with
emacs -Q
open the file (switch to html-mode if it is not opened in html-mode) and
go to line 164. There can be a little bit different errors, but the most
common is that the lines below this line are fontified as string. I
found right now that if I do
M-g g 164
then I see the error above. However if I scroll down line by line to
line 164 then the fontification is ok.
For other versions of misfontification I am not sure how to reproduce
them at the moment.