It fixed the blanking problem, but I ended up disabling it because it broke Content-Type headers on feeds. Everything was getting sent as text/html, even when I told it not to cache the feed files.

I just took another look at it, and apparently the function WP-Cache uses to save the original HTTP headers (including Content-Type) doesn’t always pick up data if you’re using output buffering—which of course is integral to WP-Cache. The suggested solution is to flush the buffer before calling apache_response_headers(), so I looked at the code. ob_end_flush() is called right after the block that saves the headers, and the only circumstance in which it tries to write any output is if there isn’t already a Content-Type or Last-Modified header. Well, PHP is going to add a default Content-Type in the worst case, and I’m pretty sure WP generates Last-Modified everywhere.

So I moved that ob_end_flush() to just before the line with if(function_exists('apache_response_headers') ). It seems to work so far. It’s caching, it’s not pushing out blank pages, and it’s sending the correct content type on feeds.