[quote author=BlackJack link=board=4;threadid=1562;start=0#msg18928 date=1064534843]
Since there is no "previous image" before the "first image", how can this be possible? [/quote]
Exactly. It has the "use previous image's palette" byte set to true, even though that doesn't make any sense. Mugen seems to be smart enough to ignore this, though, and hence sffextract needs to be able to deal with it too.
If you're curious, a couple example SFFs I found with this issue are Splode's Hiryu and Deuce & Kitsune's Geese. (If Kitsune or Splode are reading this, I'd be curious to know how you compiled the SFFs.)

[quote]Is it this rare case when there are, for examples, 2 images with the same number?
[/quote]
No, we haven't gotten around to dealing with that problem quite yet.