To reproduce:

1. Download and open attached "sprite_packer_error.zip" project.
2. Select your platform to be either WebGL/Standalone/Android.
2. Open Sprite Packer.
3. Pack the sprites by pressing "Pack" button.
4. Notice that sprites were correctly packed.
5. Go to your project location on the computer, then go to Assets folder and find "IconLock.psd.meta" file.
6. Open it with text editor of your choice.
7. In the .meta file find your currently selected platform and change its maxTextureSize property from 2048 to 128 and save the file.
8. Get back to the editor and Pack the sprites again.
9. Notice that "IconLock" sprite is now corrupted in the packed sprite sheet.

Expected result: Changes made in the .meta file do not affect the s in Sprite Packer if Override flag is disabled for that platform.
Actual result: Changes made in the .meta file corrupts the sprite when packing it with SpritePacker, even though override flag for that platform is disabled (set to 0).

Reproduced with: 2018.2.0a1, 2018.1.0b6, 2017.3.1f1, 2018.2.1p3, 2018.1.3p1, 5.6.5p1, 5.5.6f1.

Notes: When override flag is set to 1, then sprite is packed correctly in sprite packer. In Unity 5.4 .meta file structure is different and it prevents from such issue happening. There override flag cannot be edited in .meta file, the information about the sprite for that platform only appears when "override" option is selected in editor.