I am not quite sure about the expected behaviour. To select row 5 and column D at this time I can click on row 5 and then control-click on column D.  I would like to retain this possibility. If control-click toggles the selection state this would not happen. Perhaps we should use ctrl-alt-click for toggled selection.

If B7 is selected and one ctrl-alt-clicks on B7 what should the behaviour be?

After a ctrl-alt-click-drag what is the edit cell going to be? (If the click was in an unselected cell it would make sense to make it that cell; but if the cell was selected it becomes unselected so it cannot be the edit cell or can it be.)

I note that in Libreoffice Calc only ctrl-click toggles selections while ctrl-click-drag does not. That seems to be inconsistent. In LOCalc only ctrl-click on a single cell toggles. If you ctrl-click on the edit cell you can create a selection that does not include the edit cell.

I was wrong, in LO ctrl-click-drag may also de-select but it does not toggle Whether it deselect or select depends on the state of the cell first clicked on. Ie ctrl-click on a selected cell followed by a drag unselects all those cells in the drag region, ctrl-click on an unselected cell followed by a drag selects all those cells in the drag region.

We really need to define our desired behaviour...

In LO the result of ctrl-clicking on a row or column header seems to depend on whether the entire row or column was selected or not.

Personally, I am more interested in cell (un)selection.  If I select several areas and by error I select another cell (or a wrong area), there is currently no possibility in gnumeric to unselect that cell.

I sort of understood that from your report. But if we fix something we may want to fix it correctly. If we want LOCalc-type behaviour we can in fact use ctrl-click.

This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.

Thank you, I see that many lines changes in the commit!