Cannot uncheck QCheckBoxes in my C++ Qt application

I have tried setChecked and setCheckState but to no avail. I am able to check a QCheckBox but not uncheck. Everything else is working perfectly.

Debug mode was no help; installed a pushbutton to manually clear the checkboxes; tried making the boxes non-exclusive, then unchecked, then exclusive but no success. The only time I have all boxes unchecked is at the beginning when I first load the data. But then, as soon as a box is ticked that same box stays ticked unless I tick another box. But I need all boxes cleared with every fresh data insertion. My data consists of "pages" stored in a QList object. There is nothing in the pages that pretick the boxes.