visual studio 2013 extension and xml syntax coloring seem not to be able to work together.

Hello all,

I built a VS2013 language service for an xml-related language. 

This extension works properly as long as I do not define xml syntax highlighting for files having the relevant file extension.

As soon as I do that, the extension doesn't work.

Does anyone have a clue as to how I could make them work together?

Thanks in advance.