I use Saxon 6.5.2.
If I have the same namespace URI for the input and (default) output namespace (I transform XHTML --> XHTML), I can't get rid of the xmlns:html attribute in the top-level output element. This makes it impossible to create valid XHTML from XHTML.
Is this behaviour correct? Is it different in Saxon 6.5.3 or 8.x?
You'll have to give some indication of your input, your stylesheet, the output it is producing, and your desired output. Getting the right namespaces in the output can be a delicate business and it's impossible to give advice without knowing exactly what you are doing wrong.