register-timer-recurring-call doesn't appear to be recurring

If I do

(initialize-timer)
(register-timer-recurring-call 2000 (lambda (&rest args) (format t ";; *** called with args ~S" args)))

I believe I should be seeing a message printed roughly every two seconds, right? I see it printed once, after about two seconds. But then never again. I've left it running a couple of minutes without ever seeing it printed again.

This is in SBCL 1.5.5 on Linux (64 bit), running under Slime.