When selecting multiple textures that are set to "crunch" compression with different Compression Quality Amounts and making a change like Texture > Normalmap, or size, or another other changes and hit apply will result in all textures becoming -1 compression quality.

To Repro:

1. Open Unity & Attached project.
2. Select 'Texture A', 'Texture A 1' and 'Texture A 2'.
3. Make a change in the inspector like "Create from Greyscale".
4. Hit Apply, wait a while for them to crunch.
5. Observe each texture will now have -1 crunch.

On occasion these errors are thrown:

InvalidOperationException: Operation is not valid due to the current state of the object