Documentation says "Note: There might be minor issues in quirks mode (no <!DOCTYPE> specified). It works but there might be a bad pixel here or there."
However, in case of the Scheduler (v 5.0.1556) there is "a bit more" bad pixels. :-) Scheduler gets broken in Quirks mode in IE7. Just delete doctype in the demo master page and see. This can be a problem when using Scheduler inside a page template that cannot be changed.