priority of <xsl:variable ...> and xsltproc --stringparam

Hello,

I recectly installed a new xsltproc 1.1.0(?).  With the old
version 1.0.29(?) I HAD in my .xsl to declare a variable with
<xsl:variable name="foo"/> to be able to assign a value at
the command line (using option --stringparam foo bar).  With
the new version this leads to desaster, because the empty
declaration overwrites the command line value.  So I removed
the declartion from my .xsl.  Questions:

- Which of the two different behaviours is the "correct" one?

- Which behaviour do I have to expect from future versions of
  xsltproc?

- How to other XSLT processors behave, if they have the
  feature '--stringparam'?

Thanks in advance!

Cheers, WB