With an HTML form, that uses POST submission to a URL with GET style
parameters eg.
<form action="foo.html?id=10" method="post">
inks submits it to "foo.html"

This is wrong, the form should be submitted to the action URI.
That is has a query part is irrelevant. In fact, the same is
even true of method="get" - the new query string is simply appended,
separated by another question mark. I suppose that
<http://www.w3.org/TR/1999/REC-html401-19991224/interact/forms.html#h-17.13>
is probably the most relevant link here.

David