Music 5000 ROM/Disc incompatibility

[Malcohol]

The Staff Editor in the built-in Music 5000 disc doesn't work. The contents of the staff editor are not persisted after leaving the editor. This is a known issue which apparently affects real hardware, so it's not an issue with the emulation. Instead, it is apparently caused by an incompatibility between the Music 5000 ROM and the disc. See this discussion: https://stardot.org.uk/forums/viewtopic.php?p=24608

The bug can be demonstrated as follows:

1. Select the Staff Editor from the main menu
2. Press Tab to enter the editor
3. Press Return a few times to enter some notes
4. Press Tab to enter command mode
5. Press Tab to re-enter the editor
6. Observe that the notes have disappeared.

Since jsbeeb bundles these, and it might in theory be fixable by finding a valid combination, I thought it made sense to log it as an issue.