Maybe be not a bug, but imho a very weird behavior. Start with a perspective view and rotate the cam to simulate a top down view, everything is as expected (-Z goes up, +Z down). But if you switch to the actual top view mode, everything is flipped (basically rotated by 180 degrees) and -z suddenly points down.
Thanks for this odd one, in the database.
Thanks for the report. At some point awhile ago the Top and Right views got flipped so that they were actually looking at the bottom and left sides. This has been fixed now and the patch will be in the next experimental release.