Screenshot file selector should use the classical Gnome file selector available in all other Gnome softwares. Currently it is confusing for users, and the selection of folder is buggy when done by keyboard access. That's also an accessibility problem.

Steps to reproduce:
* take a screenshots with <imp_screen>;
* select a folder, e.g. /tmp by typing: <tab><space><up><up><enter>/tmp<enter>
* validate with <enter>

What do you expect to get: receiving a Capture.png in /tmp

What do you really got: receiving a Capture.png in Desktop

Imho the best fix should be the use of the Gnome file selector.