index-mobile.html – what is this?

I had a look in the contents of the WP-Super-Cache and i am seeing this files:

http://www.domain.com/title-of-my-post/index-mobile.html

http://www.domain.com/title-of-my-post/index-mobile.html.gz

Obviously these links do not exist and give 404 errors.

Questions.

1) What is index-mobile.html and index.mobile.html.gz

2) Why are they appended to the end of some random posts?

3) Surely the Rejected User agents should have prevented these requests from bots?

http://wordpress.org/extend/plugins/wp-super-cache/