@
davidfor - I'm also on Windows 10. In following screen shot, I had row 6 selected (highlighted), then I clicked the row number 17 (that is the row number itself), you can see the 17 is italicised. But the row that looks like it's selected is is still row 6. If I press left arrow then row 17 will be highlighted.
If I click on a column (authors, title etc) the row is always highlighted, and because I have the tweak set to do_nothing there's no danger of getting into edit mode or opening the book etc.
In the 4-5 years I've been using calibre on Windows, I can't recall it being otherwise. I've just assumed it's a Qt quirk.
FWIW: if I double click the row number, the format file that is highest in the preferred input pecking order is opened. I'm not sure of there's tweak to control that.
BR