(Solved) Precise behavior of Quick Import GIF Frames wrt transparency

[duckwizard]

I have some animated GIFs that I exported from an SCI game.  I have been trying for hours to get them to import properly using Quick Import GIF Frames and I can't quite seem to get it right.

First of all, the reason that I'm using GIF frames is that the SCI export tool positions each frame within the animated GIF properly so that I won't have characters moving around within the loop when they're not supposed to.  So if I can figure out how to use the GIF frames feature properly, it will save me a lot of time in the long run.

First problem: Stuff from previous frames shows up in subsequent frames, if the subsequent frame is smaller than the previous one.  This one can be solved using Filters -> Animation -> Unoptimize in GIMP.  Took me a while to figure that one out.

Next problem: Transparency.  My game is in True Color mode.  Obviously the GIFs are indexed color.  I have tried every combination of:
1. Make the transparent color be the first palette entry.  This didn't work; it just makes it black where it should be transparent.
2. Making the transparent color be the first palette entry, AND making sure it is #FF00FF even though it displays as transparent.  Same as above.
3. Making no transparency in the GIF and filling in #FF00FF instead of transparency.  Now I just get sprites surrounded by #FF00FF.

I have always made sure that the top-left pixel of each frame is the color that ought to be transparent.

So my question is: what is the precise behavior of this utility?

Edit: (before I even finished posting) I think I figured out what I was doing wrong.  "Quick Import" seems to take the transparency settings that you last used.  I couldn't find documentation on that, but I had previously imported a sprite with "No Transparency", so manually importing a sprite with proper transparency settings and then re-importing my GIF frames (with #FF00FF filled in to transparent areas) has solved the issue.  I'm going to post this anyway in case someone else has the same issue and does a forum search.

For SCI-exported GIFs, the Unoptimize filter in GIMP seems to be sufficient for good import (i.e. you don't have to fill in #FF00FF everywhere).