In windows 11, IDE 2.0.0-rc9-20220801 I had 2 files open in the IDE with same name but one starting lowercase, the other uppercase. I deleted the lowercase file and both instances where deleted from the file system.
How did you delete? Windows explorer? There is no option to delete files in RC9 as far as I can see.
How did you manage to create two files with only a difference in capitalisation in one directory?
I am updating a set of sketches replacing a .h file, the file has the same name as the old the only difference is it starts with uppercase.
So I copy the file to the directory of the sketch while the sketch is open.
The file shows up in the IDE automatically. Then I have to files in the IDE one with lowercase and one with uppercase. You can then select the old file and a 'X' apears next to the file from there you can delete the file (lowercase) and both instances are gone from IDE and directory.
I have a file abc.h in my sketch directory. I try to drag a file Abc.h from somewhere into the sketch directory using file explorer and Windows 10 only allows me to replace.
After that in file explorer
I think it's a bug that the tab with the lowercase abc.h was not removed from the IDE. But it might depend on the sequence in which Windows does its actions whether you see both *.h files or only one (that happened when I tried a cut-and-paste).
It's not a bug that both files are gone as there was only one in the first place (see the explorer screenshot).
PS
I did figure out how you delete; you delete a 'tab'
I only managed to get it like this (IDE screenshot) by dragging a file, not by cut-and-paste.
[edit] but also not consistently I think that you were just unlucky that both files showed.