Pasting map geometry inside a sector creates incorrect new sectors

[eevee]

Start with this:

Now select the inner sector and copy it. Paste it inside the same enclosing sector, like so:

The new sector is impossible to select, and trying to mouse over it will instead highlight the containing sector:

This turns out to be because the new sector's back lines — the ones facing the containing sector — all belong to a new sector that doesn't exist anywhere else, rather than belonging to the existing container.

Pasting into a different containing sector has the same result. Pasting geometry with a one-sided perimeter into a sector also has the same result.

Curiously, if I paste so that the geometry straddles two existing containing sectors, everything works fine.

[eevee]

This also happens when moving an inner sector from one containing sector to another. A similar problem occurs when copy/pasting a "hole" within a sector.