[racket] BIG BUG! On Windows, copying a bitmap doesn't work

I gave my students a bunch of images created with 2htdp/image to try
to recreate.

All of the images involving bitmaps appear as black circles on Windows.

Even if you create the image in the interactions window and then copy
it into the definitions, the same big, nasty black circle appears.

This is true on both 5.0 and the latest nightly build.

Todd

P.S. Works fine on Linux, as far as I can tell. I can have my TA check
Mac OS after tonight's class.