If you look inside of your Magento system.log from time to time, you will notice an error there like the following one:
2011-01-12T14:16:52+00:00 DEBUG (7): HEADERS ALREADY SENT:
Call stack is here..
As you may already know, it can take a lot of time to find the place where the issues like this one appeared. So, let’s investigate why it happens and what we can do to speed up the bug fixing process.