Unexpected diamond note heads

When I use ‘paste into new voice’ I find I’ve got diamond note heads at the wrong pitch ( copied from tenor ‘A’s to piano’ 'B’s) .

What’s more if I use edit “Edit > Notations > Notehead” I find that resetting to default notehead doesn’t do anything . Nor can I see anything spectacular in the properties panel.

What does it mean? how do I fix it ? many thanks :slightly_smiling_face:(as always)

Actually I’ve just understood this it’s some kind of slashed voice!