If you go to a network path that cannot be resolved immediately (typical Windows issue) and you'd like to cancel that by closing the tab, clicking on its (X) button completely closes DOpus (I don't even think it crashes).
The X on the tab itself, or the X for the whole window (which can be configured to close tabs)?
Windows might kill the whole process if the X for the whole window is clicked sometimes, usually if it things the app isn't responding. The X for an individual tab shouldn't normally close more than the tab.
Were any crash dumps created matching the time this happened?
The X on the tab.
Where are DOpus crash dumps stored?
P.S. It's not a new issue. It's been here for years.
Do you have Preferences / Folder Tabs / Options / Lister closes when last tab closes turned on?
Maybe you should have reported it years ago then 