The bug

If a resource pack is applied that wouldn't need as large of an atlas as the previous resource pack, the previous size of the atlas will be retained. (MC-263119) This can have some unwanted side effects.

How to reproduce

A resource pack that expands the blocks atlas to 16384x16384 (the maximum size) is attached to this ticket.

1. Download this resource pack
2. Observe an enchanted item
3. Apply this resource pack
4. Then remove this resource pack
5. Look at an enchanted item again
6. Press F3+S

Expected results

Removing the resource pack would revert the atlas to its previous size, so pressing F3+S would produce a 2048x1024 blocks atlas in the screenshots folder. In addition, enchanted items wouldn't look any different.

Actual results

Removing the resource pack does not revert the atlas's size, so pressing F3+S causes the game to produce a 16384x16384 image file, which takes a very long time. In addition, the enchantment glint looks different now (MC-276841).

How to fix

The needed atlas size should be recalculated every time the resource pack is reloaded and shrunk accordingly to avoid this issue.

Further notes

The attached texture atlas file has been run through FileOptimizer as to fit within the file size limits, and therefore is not the original 12MB size.