Assertion failed with insert after in a collection

The following query crashes zorba with an assertion failure:

import module namespace ddl = "http://www.zorba-xquery.com/modules/store/dynamic/collections/ddl";
import module namespace dml = "http://www.zorba-xquery.com/modules/store/dynamic/collections/dml";

ddl:create(xs:QName("ddl:test2"),(<center1/>,<oldlast/>));
dml:insert-nodes-after(xs:QName("ddl:test2"), dml:collection(xs:QName("ddl:test2"))[1], (<c1/>,<c2/>));

dml:collection(xs:QName("ddl:test2"))/self::node()

Also

import module namespace ddl = "http://www.zorba-xquery.com/modules/store/dynamic/collections/ddl";
import module namespace dml = "http://www.zorba-xquery.com/modules/store/dynamic/collections/dml";

ddl:create(xs:QName("ddl:test2"),(<center1/>,<oldlast/>));

dml:insert-nodes-before(xs:QName("ddl:test2"), dml:collection(xs:QName("ddl:test2"))[2], (<c1/>,<c2/>));
dml:collection(xs:QName("ddl:test2"))/self::node()