Saxon

The immediate cause is that method ExpressionInverter.returnsStreamedNode() returns true.

The problem can be fixed for this case by changing this method to extend the test for "type = atomic" to "type disjoint with node". Since result-document returns nothing, this test will cause the method to return false.

However, this doesn't seem to address the root cause of the problem. The code for computing the path map of the result-document instruction seems wrong (in fact, it's using a default implementation). Looking at the path map of xsl:element and xsl:document, that seems to be better, but still not quite right. Unfortunately the path map code is complex, has been unchanged for a long time, and there aren't many tests that will show it up if it's wrong; so changing it is precarious. For 9.5 I'll put in the immediate fix above and leave the deeper problem to fester for a while.