XML : Attribute extension in XSLT task doesn't work

Here is the problem:

I have an XSLT task that suppose to produce an XML file as output. This is the output I am currently getting:

C:\Users\rmrd001\git\xslt-framework\examples\intermediate\odt-folder\t2\t2.1\content

It produces a file without any extension. So the windows doesn't provide default program to open with. Of course, desired result is same but with extension included. Namely:

C:\Users\rmrd001\git\xslt-framework\examples\intermediate\odt-folder\t2\t2.1\content.xml

And here is the task definition:

  <xslt in="@{file}" out="${dita-odt.path.odt-unzipped-base-dir}/${common-path}/${file-base-name}" style="${dita-odt.path.text-odt-xsl}" extension="xml" force="true">                              <param name="dir-path-styles-xml" expression="${dita-odt.path.odt-unzipped-base-dir}/${common-path}"/>                              <!--The following parameter is designated for reference nodes that require absolute path. For example draw:image/@href. This is to achieve system portability as well.-->                              <param name="project-base-dir-absolute-path" expression="${base-dir-unix}"/>                              <classpath location="${infrastructure-base-dir}/${dita-odt.text-odt-xsl.processor}"/>                          </xslt>    

I know this is not the complete script, but everything works fine except the extension missing for the output document. There is no mapper nested into the XSL task. I can also work around it by adding .xml to the path specified into the out attribute like this out="${dita-odt.path.odt-unzipped-base-dir}/${common-path}/${file-base-name}.xml". Anyway, why it doesn't work?