Just tried with slick V20.0.3 and didn't see a problem.
Maybe the file tab sort order is confusing you. Right click on a file tab then down the bottom of the menu there is "sort order". Try changing it to "manual".
What happens if you open a new file using the workspace tab of the file tool-window.
If you can't get it working, close slick, make a copy of vslick.sta from you config folder, then delete vslick.sta and restart slick.
Alternatively, export all your config options via tools -> options -> export / import, then import them into a brand new empty config folder.