[plt-scheme] frtime repl question on 3.99

I'm doing some play with FrTime.  The following program:

     (define-struct s (t))
     (define mytime (make-s seconds))

runs, but when I try to display mytime in the interaction repl, there's no 
response, and from that point forward after I do a user break, reactivity 
seems to die until I rerun the program.

Is this expected behavior?  Should I just be careful not to display 
structures with signals in them?