I've started using MMM-mode in XEmacs for working with php/html blended pages. Normally, this works just fine, but I opened a file just now that was around 500 lines entirely enclosed in <?php ?> tags, and every single time I type a key inside, the entire thing refontifies.
Before I started using mmm-mode, font locking happened on a per-line basis. As in, if I typed an opening quote, the following lines wouldn't change their current highlighting. Now, when I open a quote, everything below it changes to my string font until I insert the closing quote.
I've tried reading the mmm .el files, but it's been a long, long time since I've done anything in elisp, and I'm not seeing a good way to disable the constant reprocessing of the buffer.