Polar Coordinates and Panorama Projection filters leave gap after being applied.
In GIMP 2.10.20, running on windows 10, and since version 2.8.20 I think, there's a bug in the Polar Coordinates filter, that leaves a gap in the image after being applied, and a small displacement: it's expected that the two horizontal ends of a image meet eachother after the filter, but it always seems to have a small displacement, with one side "lower" than the other, which is a problem when working with seamless images.
However, if the "Map backwards" box is checked the gap seems to close but it still has the displacement.
Gaps also show up when the inverse transform of the panorama projection is applied to images, when creating 360 images: Here the gap is in black, below the red and magenta squares