K-SeqExprInstanceOf-59 is as follows:

(error(), 1) instance of empty-sequence()

It can be statically inferred that the type of the argument is (none, xs:integer) and so this query could be optimized down to:

false()

However the test expects an FOER0000 error to be raised.

K-SeqExprInstanceOf-62 and K-SeqExprInstanceOf-63 also both expect an error to be raised when the result of the instance of expressions can be deduced statically.