Skin model resets to “Classic” even after uploading Slim skin (model flag not saving)

When uploading a Slim (Alex) model skin on the official http://Minecraft.net profile page, the model type reverts to Classic after refreshing or logging out/in again — even if a Slim-format PNG is used.

The issue persists across browsers and devices, and clearing cache does not help.
The in-game model also appears with Classic arms, confirming that the “slim” model flag is not being applied to the player’s account.

Interestingly, third-party sites like NameMC show the skin as Slim, suggesting that the old flag may still exist in cached texture data, but Mojang’s live player profile API (and the game client) are defaulting to Classic.

Steps to Reproduce:

1. Go to https://www.minecraft.net/profile

2. Upload a Slim-format skin (64×64, 3-pixel arms)

3. Select Slim model and click Save

4. Refresh the page

5. The model type automatically switches back to Classic

6. Launch Minecraft Java Edition → observe that the player model in-game has Classic (4-pixel) arms

Expected Result:
The selected Slim (Alex) model should remain applied both on the http://Minecraft.net profile page and in-game after refresh.

Actual Result:
The model reverts to Classic, even though the uploaded skin file is in Slim format.
In-game, the player model uses Classic arms.
NameMC and other skin viewers may temporarily still show Slim due to cached data.

Additional Info:
I have attached the skin file as an example.