I find I’m constantly, reflexively clicking the “Post this comment” button when I mean to attach a file. I think it’s because the button looks similar to the ””Choose file” button, and my unfocused, multitasking mind thinks I’m clicking the thing that lets me browse files I want to attach.

I suggest you use a small GIF icon of some kind next to the text link “Attach files to this comment”, which tends to be easy to ignore when you’re working quicky.