I have run into a very confounding problem with InDesign CS5.5.
I've tagged my document with an XML structure, but when I export the XML, InDesign includes a whole block of text that doesn't exist in my document.
I checked the text, the master pages, the layers, everything I can think of.
If I enable "Show text snippets" I can see the text in the top-level element, but it doesn't exist anywhere in my document.
Hitting "Select All" on my document selects only the 'div' node and below in the structure panel.
The phantom text is from another document that I was working on the last time I tried to work with XML in InDesign.
Had the same problem. Ended up stripping the XML and reapplying to get rid of it.