[Update: I messed up some code. Corrected version now]

Greeting from the frigid city of Redmond. Keep in mind, of course, that in the Puget Sound region, "frigid" is any temperature below freezing.

Thanks for all the feedback on previous bad code examples. I've created a new category for these posts, so you can avoid my other posts if you wish.

This snippet is a routine that is used for web debugging.

enum ResponseType { ReturnValues, InvalidInput }

string CreateWebText(string userInput, ResponseType operation) {
   switch (operation) {
      case ResponseType.ReturnValues:
         userInput = "<h1>Values</h1>" + FilterOutBadStuff(userInput);
      case ResponseType.InvalidInput:
         userInput = "<h1>Invalid</h1>" + FilterOutBadStuff(userInput);
   return userInput;

What's wrong with this code?

Hint: There are both obvious and subtle issues lurking...