mycheckbox.setSelected(false) has no effect

I have columns of checkboxes, the top row of which are CheckAll checkboxes for that particular column. If I uncheck the Checkall from the first CheckAll checkbox in the leftmost column I would like to uncheck the remaining CheckAll checkboxes.

However the mycheckbox.setSelected(false) has no effect. If however, I do a mycheckbox.setEnabled(false) (just as a test) it DOES work and the checkbox is disabled.

By the way, this is a "header row" for a listview with a custom adapter. The contents of the listview work as expected.

Any idea how to get the checkbox unchecked?