I am using Frames Modify->Replace selection(source is the active frame), from Photocomix Windows GIMP compilation, but for whatever reason, the selection is not being copied to the specified frame:



Sometimes it works, sometimes it doesn't. I haven't figured out what makes it work.
Any suggestions?

I don't know well the function and i have not the gap doc at hand
i suppose you need a selection in order to replace it but is just a guess

all what i may do is search for a recent copy of the gap doc where is explained how the various filters work

FOR THE MODS :

Ib case the Gap doc may be hosted somewhere on GC ?
it is a txt file , not to nice to read because is not formatted text and with no any illustration , anyway explain all gap function and is not too long (and since is only txt is a very light file )

Your screenshot shows the active frame, "from" frame, and "to" frame all being the same frame (#23). "Frames Modify->Replace selection" skips over the active frame (why copy the selection to itself?), therefore nothing should happen.

The selection is for one frame, ergo it does apply it to that dialog chosen frame(from the current calling frame's selection). Sometimes it works, sometimes it does not.