[eluser]luismartin[/eluser]
Hey Cronix! Thanks for your explanation. I see. Yes, that timestamp within the cached file is redundant. So, when there is a first ajax request for content X, CI creates the corresponding cache file, adding the timestamp at the beginning, but the output is not dumped into it. So in the next requests for content X (I guess whether they're ajax or not) there's no content to display. Blank.
This issue has led me to another question:
Why CI behaves this way when the request is asynchronous? Why doesn't CI dump any output html into the cached file? I'm using views to generate the output, which in turn is delivered to the controller, and this one sends the headers and echoes the output.