2.2.5 [W3C-XSLT] Section 7.1.1, Literal Result Elements
The specification states:
If a namespace URI is declared to be an alias for multiple different namespace URIs, then the declaration with the highest import precedence is used.It is an error if there is more than one such declaration. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing,from amongst the declarations with the highest import precedence, the one that occurs last in the stylesheet.
MSXML3 and MSXML6
No error is signaled. Instead, the last matching template rule in the style sheet is chosen.