Effect of default namespace specifications on imports

I am writing an XML conversion, part of which entails bringing things
into the new namespace (from no namespace).

I have specified namespace X as my default namespace and my XPath
default namespace but all is not as expected.

I suspect it is because some elements are handled by an imported
identity template. Although this can be worked around this represents
an opportunity to get some clarification as to what the precise rules
are as relates to default namespace specfications and imported
stylesheets.