Brush Clipboard Mask feature doesn't working correctly with selection shapes
GIMP version: 2.99.1
Operating System: Linux, Fedora 28, GNOME
Package: from git
Description of the bug
When you try to feed the brush clipboard with a free selection or another regular shape, e.g., a circle, the 'Clipboard Mask' doesn't follow the selection shape... always the figure is shown as full square, where the side measure, of this square, is the more large dimension find in the selection. I have tested also with(1) and without alpha(2) channel with a background color, also tested in a transparent layer(3)... and we have the same issue in all three cases
Expected result: as occurs with Clipboard Image, where the selection shape is obeyed by the feature.