Has the bug occured in previous versions? If yes, please specify version(s): (This option is optional, and doesn't need research. But in case you know...)
Description of the bug:
The pattern editor has a refresh bug.
How often does it happen?:
How to reproduce (step by step description):
1. Open the pattern editor.
2. Open the song properties dialog.
3. If a scrollbar is present, reduce the number of channels (I used 1).
If everything worked "properly,'' you should still see (and be able to use) the scrollbar.