[plt-scheme] DrScheme debugger pops up new window

Hi folks,
    I'm using DrScheme 371. Everything is fine until I hit the Debug
button. A new DrScheme window then popped up, containing the same
source code as the old one. The old window was then under debug mode,
and the pause/continue/step... buttons showed up on the toolbar. But
whenever I click one of these buttons, a new window popped up just
like the first time I clicked the Debug button.

    Does anyone have any ideas about this? I don't know if it's a
feature or what. It's quite annoying.

Thanks in advance.
   Harry