This seems like a bug:
Pike v8.1 release 13 running Hilfe v3.5 (Incremental Pike Frontend)
> (<"foo", "bar">) | (<"some", "bar">);
(1) Result: (< /* 3 elements */
"bar",
"foo",
"some"
>)
> (<"foo", "bar">) + (<"some", "bar">);
(2) Result: (< /* 4 elements */
"bar",
"bar",
"foo",
"some"
>)
>
--
Stephen.