There are countless issues with the animated gif filetype plugin..
Issues
Lack of transparency support
Quality severely damaged by this plugin
Importing creates a layer for each frame, but moving the image in the layer ( ie to center in resized canvas ) creates a duplicate of the frame so you have to go back and remove others ( I also tried without removing in case it was a mask, but transparency still escaped the saved file even if I tried apng or agif instead of gif )
Lack of options during save phase ( It should have gif options, ie transparency PLUS current 2 options )
I tried another which doesn't downgrade quality but has the same issue with transparency... Am trying out masking in paint.net with another addon, hopefully it won't show up as an extra frame or so......
Any solutions? Am going to try the alternative suggested by midora shortly.