ARQ casting and XPath spec

[Bob DuCharme]

In ARQ 2.8.8, it looks like xsd:boolean(4) returns nothing, but 
according to http://www.w3.org/TR/xpath-functions/#casting-boolean it 
should return True. Also, 
http://www.w3.org/TR/xpath-functions/#casting-to-integer says that 
xsd:integer("true"^^xsd:boolean) should return 1, but it doesn't return 
anything. The table at 
http://www.w3.org/TR/2012/WD-sparql11-query-20120105/#FunctionMapping 
says that these two casts are always allowed.

Is this an ARQ bug, or am I misunderstanding some aspect of the specs?
thanks,

Bob