Suddenly, my stacks won't collapse. Files that indicate that they are stacked in the Viewer won't collapse now. I can see all files in the stack displayed in the viewer and the topmost file in the stack shows the number of files in the stack but when I click on the "number of files in the stack" indicator, the stack won't collapse. I tried selecting all files and doing right-click "Stacking->Collapse" but nothing happens.
Is there some key combination that causes this?
Have you enabled the File Window option to always show stacked files?
See "Show stacked files" in The File Window Toolbar (https://www.photools.com/help/imatch/fw_basics.htm?dl=hid-3)
That was it. Thank you.