Font lock problem with XML, HTML documents

[Wellie W. Chao]

I'm having a problem in which emacs doesn't properly fontify XML and
HTML files if I load them in a certain order. The weird thing is that
XML and HTML files are properly fontified if I load them in another
order.

[*] If I load an XML file, emacs reports that psgml has been loaded.
The file is not fontified. If I then proceed to load an HTML file, the
HTML file is not fontified either. I also get an error from emacs:

File mode specification error: (error "Key sequence C-c C-c - uses
invalid prefix characters")

[*] If, in contrast, I load the HTML file first, it is properly
fontified. If I then load the XML file, it is also properly fontified.
All further loads of HTML and XML files, regardless of the order, are
successful and result in proper fontification.

Anyone know how to fix this?