Blog refers to the "URL friendly title" field in the bar right of the blog post editor.
It's prefilled by a suggested URL. I usually overwrite those URLs to more SEO-friendly ones.
When I type in the dialog, most characters I type are NOT registered.
I have to type very slowly and still repeat some keystrokes several times until they are registered.
My go-to solution is typing out the URL somewhere else, then copy + pasting it to that field.
PS: "URL friendly
title
" is a misleading name for this. Should be called "slug" or simply "URL" or "Post URL".