I had to do a bit of digging around on my current project to help resolve a strange HTML issue we were having with the XSLT List View Web Part (XLV). In the end I tracked it down to the fact that if you have enabled the AJAX Options for the web part then the contents of a list are rendered differently!
In these screenshots notice the dropdown arrows on the column heading. It’s different! The underlying HTML is pretty messy so not something I’ll bother listing here (the AJAX version has a whole other table embedded!) – but the fact that it’s different could potentially cause you problems (as it did us) in that any custom CSS you have may need to be aware of this.
Hopefully that saves someone the headache of trying to track down why you have different rendering for your XLVs!