Get the editor split. Open files A, B, C in tab group 1, and files C, D in tab group 2.
In tab group 2 close file C. It works well.
Close (the last) file D in group 2. D is closed, but C opens in group 2.
Close (the last) file C in group 2. C is closed, but B opens in group 2.
Close (the last) file B in group 2. B is closed, but A opens in group 2.
Close (the last) file A in group 2. File A is closed in both tab groups.
Looks like serious regression, so, critical.
when the same file is opened in both splitter sub-windows, closing the editor in one sub-window closes it in the other one.