To reproduce:

(iter-next (funcall (iter-lambda () (pcase (list 1 2)
                                      (`(,a ,b) (iter-yield (+ a b)))))))

Patch is attached. I have no idea if it affects something else, but
matching symbols with `eq' on their names (`eq' on strings?!) seems
outright wrong to me.

On a side note: bug report I sent yesterday with M-x report-emacs-bug
was silently lost.

Paul