It's inside the editor component. Trim trailing spaces behavior is strange, it trims when you leave the line (Enter, arrows, mouse) When you connect it with enabled step behind the EOL (end of line), when you can put cursor anywhere behind the real line end and the position is virtual till you write some letter it's hard to fix it without break other functionality.
If you remember, I tried to fix inserting real tabs instead of spaces and it broke undo/redo and cursor positions (your last emotional e-mails) ;-) -- <https://forum.pspad.com/read.php?6,74752,74817> PSPad freeware editor https://www.pspad.com
