In order to help us determine exactly the cause of this behaviour, could you be more specific about the context? Which version of Adobe Campaign do you use? Is your email content imported using “DCE” mode? And which part of your code is stripped out (is it all of what you pasted here?)? Also, at which moment do you notice the code of the email has changed?
Sometimes when importing content in DCE editing mode, parts of the code can be automatically re-written for deliverability and compatibility purpose. If this is what you’re experiencing, please contact Adobe support to escalate the problem as this is a known behaviour.
If this is something different, do not hesitate to post more details here so that we can dig into it together.