Except I'm mistaken, the actual archive version of Font Awesome is 3.1.0 on the website.
The version 3.1.1 is expected.
I tried to test the feature "Stacked Icons" with the actual version, but it's not working
Could you please check and update the archive ?
Thank you in advance for your feedback ?
I don't know what an archive version is. You mean the zip file? How are you determining the version?
I opened archive downloaded from the website http://fortawesome.github.io/Font-Awesome/, then the file font-awesome.zip\font-awesome\css\font-awesome.css.
And I could read this string : Font Awesome 3.1.0
I think the archive is not updated.
It was an oversight on updating that version. However, this causes no problems as that version string only drives caching for the font. Since the font files did not change between 3.1.0 and 3.1.1, this is not a problem.