Tilesets: Match Corners does not set tiles correctly when erasing tiles.

[alpanumei]

Tested versions

Reproduced in LTS 26.2 Stable

System information

Redot v26.2.stable - Linux Mint 22.3 (Zena) on X11 - X11 display driver, Multi-window, 2 monitors - OpenGL 3 (Compatibility) - AMD Radeon RX 5500 XT (radeonsi, navi14, LLVM 20.1.2, DRM 3.64, 6.17.0-35-generic) - AMD Ryzen 9 3900X 12-Core Processor (24 threads) - 31.24 GiB memory

Issue description

When setting up a 2x2 terrain set using the Match Corners mode, erasing tiles does not correctly set the surrounding tiles the first time around. This issue is not present for the Match Corners and Sides Mode.

Steps to reproduce

1. Import the attached files into an empty project
2. Ensure files have imported properly
3. Open tile_map_layer.tscn in the editor
4. Select the contiguous region terrain mode in the tilemap window at the bottom of the screen.
5. Erase sections from the square. Surrounding tiles are not correctly set unless they are finagled with.
6. Switch the tileset mode to Match Corners and Sides and try again. Issue disappears.

Minimal reproduction project (MRP)

tilemap-testing.zip