XMLRPC API storePage ignores parentId=0

When attempting to remove the parent from a page using the XMLRPC API method storePage the attribute parentId is ignored. It is entirely possible I'm putting in the wrong value/type.

I am building a HastTable with a key/value pair: parentId/0

The type of the value is java.lang.String.

When the method returns the page the parentId attribute is still set to the old parentId.

If I change the parent from one page to a different page, everything works fine.

Is 0 (zero) the corrent value for a "root" page. Do I need to specify any other parameters other than parentId=0 to "unparent" a page?