Block faces using a variations terrain texture briefly show the wrong texture

Custom blocks whose minecraft:material_instances texture is a terrain_texture.json entry with variations sometimes draw a single face wrong after a nearby block changes. In the repro the face stays wrong for exactly as long as it takes the next block change to rebuild that chunk section again, then shows its own tile. The face shows one of:

• a different tile: another variation of the same entry, or a tile from a different entry

• thin stripes of unrelated colours, sometimes over a dark area (in our add-on, with the array form below, also a grid of many unrelated atlas tiles)

• a blank colour: pure white in our lit add-on, solid black or flat grey in the repro's closed room

Both the documented shape ("textures": { "variations": [...] }) and the same variations wrapped in an array ("textures": [ { "variations": [...] } ]) are affected. The repro shows wrong tiles and stripes with each shape. A face whose entry is a plain single texture is never affected. In our add-on, pointing every variations entry at its heaviest texture stopped the glitches completely.

The pack has 481 full-cube blocks in three groups, each block with its own terrain_texture.json entry:

| Group      | Blocks                                 | Entry                                                     |
| ---------- | -------------------------------------- | --------------------------------------------------------- |
| Documented | `ss_btv:doc_000` to `ss_btv:doc_239`   | `"textures": { "variations": [...] }`                     |
| Wrapped    | `ss_btv:wrap_000` to `ss_btv:wrap_239` | `"textures": [ { "variations": [...] } ]`                 |
| Plain      | `ss_btv:plain`                         | `"textures": "textures/ss_btv/plain"` (control, grey `P`) |

Entries have 1 to 18 variations, all weight 1, over 4488 unique 16x16 textures. Each documented entry has a wrapped twin with the same number of variations and the same numbers and colours. The wrapped textures also carry a white triangle in the top-left corner, so a face in a recording can be traced to its group. The plain control is one block with a single grey texture marked `P`.

Each variations texture shows its variation index in white on a colour unique to its block. The pack is sized on another affected add-on: 492 texture entries with 1 to 18 variations each, where removing some of the variations did not stop the bug. We have not tested whether a smaller pack also reproduces it.

Steps to reproduce

1. Import the attached block_textures_texture_variations_white_faces.mcaddon and create a flat world with both packs applied (no experiments needed).

2. Run /ss_btv:bug_report build. A 48 x 48 room, 8 blocks high inside, is built around you within a few seconds; wait for the command's output. Floor, walls and ceiling are a fixed pseudo-random mix in three equal shares, one per group: plain, wrapped and documented blocks stand next to each other. The command's output lists how many blocks of each group were placed.

3. Run /ss_btv:bug_report churn. Every 10 ticks it places or removes a glass block at eight spots just inside two of the walls, so the chunk sections holding those walls are rebuilt every half second.

4. Stand still and watch the walls for a minute.

1. Run /ss_btv:bug_report churn again to stop it, and watch for another minute.

Expected result

Every face always shows its own texture. On a variations block that is one of its numbered tiles, chosen by position and stable. Documented and wrapped blocks look and behave the same.

Observed result

Walls where the glass is churning, random variations blocks have their textures changed briefly then snaps back to their original texture. Sometimes the textures are either random entries, a texture atlas, or white.

Note

The Plain blocks never have their textures flicker, only the ones using variations do.