Page preview with PHP build-in server not working

[aptly-io]

I cloned grav, did bin/grav install, bin/gpm install admin and run locally with php -S localhost:8000
I had a question regarding the admin plug-in and editing of pages; with the above setup there's just home to edit. There's an 'eye' icon and I was suspecting this is to 'preview' the editing? However, when clicking nothing happens except that for a few seconds a red widget appears saying "Not found". So my question is what is the purpose of the "eye" button and why is it saying "Not found". Should I install something extra?

[flaviocopes]

Replicated on the PHP built-in server (php -S localhost:8000). Works fine in MAMP

[w00fz]

Duplicate of #3 even if this came up before :)