Bug? trying to change the voice of a note

Hello,
Normally I can select one or more notes, and then click on one of the 1 2 3 4 buttons in the task bar to change the voice of a note. This doesn't work for the second sol in attached example. When I select the 2 sols that have voice 2 and click on '1' nothing happens.
The work around now is to delete the notes and enter them again in the right voice.
Is it a bug?

Thanks,
Luc.