The first line in the screnshot below is when you type й in a new file creation dialog. The bug is: the letter is converted into two unicode codepoints instead of remaining as one:
The second line is when you type the same letter in a rename dialog, it doesn't do any conversions and remains correct as a single codepoint (curiously, in (Path)/Finder rename dialogs also have this bug)
(the different glyphs is a font bug, but still serves as a useful illustration of this Marta bug)
The first line in the screnshot below is when you type й in a new file creation dialog. The bug is: the letter is converted into two unicode codepoints instead of remaining as one:
The second line is when you type the same letter in a rename dialog, it doesn't do any conversions and remains correct as a single codepoint (curiously, in (Path)/Finder rename dialogs also have this bug)
(the different glyphs is a font bug, but still serves as a useful illustration of this Marta bug)