Looking at the code in swank.lisp, I suspect a *PACKAGE* bug in the following:

(defslimefun oneway-eval-string (string buffer-package) "Evaluate STRING in BUFFER-PACKAGE, without sending a reply. The debugger hook is inhibited during the evaluation." (let ((*buffer-package* (guess-package-from-string buffer-package)) (*package* *buffer-package*) (*debugger-hook* nil)) (eval (read-form string))))

My guess is that (let* ...) was intended so that *PACKAGE* is bound to the new value of *BUFFER-PACKAGE*.