Using -nograb is exactly what I was about to suggest.
I suspect the problem is SDL-related.
Odd that it doesn't work from the launcher, though. You're checking "Don't grab mouse/keyboard in a window" under Dev Tool?
Could you paste the contents of Diaspora/data/cmdline_fso.cfg
in a post? Use "code" tags by clicking on the
button while you're writing your post.
The result should look like this.
Where do you have Diaspora installed? Is it in a place where you have write access, that is, not in /usr/ or /opt/ or something like that?
Also, the launcher doesn't make any changes to fs2_open data files until you press Play.