"Hide empty staves" error
In the attached file, the violin part is blank and the second bar is hidden (style - general - hide empty staves).
Enter note input mode and insert another note into the bass clef of the second measure.
An error occurs. Note mode displays the note you are about to enter as being on a ledger line of the treble clef. When you enter the note, the hidden violin staff reappears and the note displays on that staff instead.
This error always occurs when there is a part (single or multiple staff) below a multiple staff part.