Color highlighting ceases on large files

[johnndavis]

I am working with an HTML file just over 1 MB in size. But for the headers, it would actually be valid XML. When the file was smaller, the color highlighting worked fine. Now, when I open the file, there is no color highlighting. I can select all the text and copy all the text to a new file, at which point the color highlighting is there. The color highlighting works fine as I continue editing too. When I save, close, and re-open the new file, however, there is no color highlighting anymore.