content folder structure:
├── 404.md
├── index.html
├── index.md
├── Pico-master.md
└── sub
├── index.md
└── page.md

Then open the /admin url
Pages shown correct in the left
When I clicked on any page on the left . the right area shown "Error: Invalid file"

I position the error on pico_editor.php line 119.
the file url is not corrent .
when I want to edit the index.md, the $file variable = Pico-master
when I want to edit the sub/index.md, the $file variable = sub
when I want to edit the sub/page.md, the $file variable = page

so I suppose this is a very big bug