Using a TextureAtlas in a Tile Map TileSet shows error for multiple files

[jself]

Godot version:
3.2

OS/device including version:
Manjaro Linux (up to date, rolling release)

Issue description:
Importing individual PNGs as a texture atlas and then trying to add them to a tile set shows the error:
"1 file(s) were not added because was already on the list"

Steps to reproduce:
Select multiple pngs, change import type to TextureAtlas on the Import tab.
Create a new TileSet and attempt to drag files to tileset.

The first one works fine, but future ones do not.

Saving a separate Atlas File and then using it as the image is a workaround, but it is more troublesome to create individual tiles if they are different sizes

Minimal reproduction project:
Attached, TileMap has one tile but dragging additional shows the error
AtlasExample.zip

[arkology]

If i understand correctly, you're talking about TextureAtlas import option in Import dock. If it's true, look #32869 This happens not only in TileSet.

[jself]

@arkology Hmm, possibly, I was able to use the Texture Atlas files elsewhere (like in a Sprite or AnimatedSprite frames) so I think this specific error may be specific to the TileSet.

I did use the Import dock to designate them as TextureAtlas files, but that part worked fine. I didn't see the error in that ticket.

[jself]

Here's the error I'm seeing after trying to drag BGTile (2).png into the TileSet

[akien-mga]

Fixed by #38388.