> combination SHOULD work:  +*.jpg -tn_*.jpg

This is incorrect, and should be:
+*.jpg -*tn_*.jpg

Remember that filter checkings are based on the 
COMPLETE URL ; that is, for example, 
www.foo.com/bar/index.html

Therefore, '-tn_*.jpg' may forbide 
<http://tn_foo.com/smith.jpg> but NOT 
<http://www.foo.com/tn_1234.jpg>

> tab is set for 'Store non html files'.

This is not advised - as this option will not store 
html files, which may not be very practical

> Aside from this little quirk, I've grown to love 
your 
> program dearly!

Thanks ;)