Internal fatal error on node insert

[Federico Cavalieri]

This query raises an internal fatal error:

variable $y:=<a>c</a>;
(
insert node "a" as first into $y,
insert node "b" before $y/node()[1]
);
$y

Zorba Internal Fatal Error in /zorba/trunksrc/src/store/naive/node_updates.cpp:943:
"theParent": condition failed