Sorry that this isn't a reply to your question, but it seems as good a place as any to post this:

I haven't liked ANY of the recent versions of 3dFibs.  Every time I try out a a new version, one or more features that I like are gone, and there are new features that I don't like at all. 

I've tried every upgrade that's come out, and so far, I'm sticking with 4.0.28.  Thanks for the heads-up -- I won't even bother with 4.0.7.0. 

I agree with you -- "auto ask repbot on invite" is an indispensable feature. 

It seems to spray files all over the hard drive more or less at random, but will usually put the .mat files in the same directory until you change something.  Try using search and looking for *.mat.  You should be able to find them that way.  That's what  I do anyway. 

Currently, it's placing them in C:\Documents and Settings\Walt\My Documents\3dfibs\jf_mat\ but previous versions saved them elsewhere.  I expect that this will change again next time I change settings or version.

As for robustness, v4 seems more stable than v3 - it's not really a problem as far as I can tell.  Remember that it's free...