Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes in xemacs-beta(a)xemacs.org: That would be me. This isn't true. I revert buffers every day (usually ChangeLogs) and they get re-font-locked. Yes, please do this. The code that handles buffer mode initialization is extremely complex and I wouldn't be surprised if you are doing something subtle in vc.el to break it. If someone wishes to take on a smallish project that we will love you for years for doing, cleaning up buffer initialization is the project. ... Undoing my patch is not the correct thing to do, but it would be interesting to see if it has any effect. Once it is undone, also try doing a `M-x revert-buffer' on a large ChangeLog file. Because normal-mode restores the font lock state. I am using fast-lock.