xsltproc param resolving

Hello,
I'm upgrading to newer version of xsltproc (libxslt v1.1.33, libxml2 
v2.9.9) and discovered the behaviour change of passing param value.
I've already realized (or at least I think so) why "--stringparam key *" 
cause the error (since it's evaluated somehow as a file search). But why 
with "--stringparam key 1" the condition <xsl:if test="$key = 1"> 
doesn't work while the number is taken? It's ok when using with 
apostrophes but it's confusing.

Thank you
Regards Jan