[plt-scheme] excessive refresh

> How do I reproduce this? I use Windows XP.

Take the following code and add the parens needed to finish the 
definition of foo. After each paren you'll see the screen flash several 
times in a row.

(define foo
   (let ([abc 123])
     (let ([def 123])
       (let ([ghi 123])
         (let ([jkl 123])
           (let ([mno 123])
             (let ([pqr 123])
               'abcdefghijklmnoqpr)

If you make bigger regions you notice the flashes even more.

Dave