I have discovered an issue caused by a new change of behavior on the Folder Tab bar.
The changelogs (13.13) are describing the change by:
You can now drag folder tabs out of the tab bar to create new windows for them (like in a web browser), without having to drag them to the Windows desktop.
Unfortunately, this means that every time I am attempting to re-order a tab, the tab becomes a window and I can't drop it by fear of having it become its own window instance.
I haven't been able to find a setting that would disable this "new" behavior.
I want this new method to work because to get the context menu shown in the screenshot, I must very carefully position my pointer in an empty part of the tab.
Edited / Update
I got it to work. I discovered that I must very precisely click the tab in an empty area of the tab - the same empty area I need to click to get the context menu shown above to appear.
Then in Preferences > folder tabs > options, I selected small close buttons, and that makes it much easier to click the tab in the right place:
You can also drag the label part, unless you have turned on Preferences / Folder Tabs / Options / Treat tab label as folder when dragged or right-clicked (which makes dragging the label part like dragging the folder itself, not the tab).
You can also increase the minimum tab width to give you more space to drag, if needed..
I'm having this same problem in 13.15
I am using a mixed-DPI system, but even after disconnecting my other monitor and restarting Dopus, I still can't reorder the tabs (it just moves it into a new window, like OP).
All the compatibility settings are off. This is a fresh windows install. I've tried uninstalling, installing checking all the compatibility settings are off, reset to factory, it still doesn't work.
If you use File > Exit Directory Opus, then restart Opus, is the problem still there?
One possible cause of the problem is tools that put a transparent window over the top of the desktop, which always make it look to Opus like the tab is being dragged to another window (since the other tool's window is covering literally everything, even if it's not visible). We saw that with a tool that displays information in overlays, for example. If anything like that is installed, try disabling it to see if it's involved.