3 Star Enhancement Scroll only gives 1 Star

This isn't a bug.

It's supposed to bring the item up to 3 stars, it does not add 3 stars to the current amount of stars. If the item is 3 stars or higher, the scroll is un-usable.

This fact is also true with 2 star and 5 star enhancement scrolls and any other enhancement specific scrolls.

Can confirm this man is correct, from personal experience.

Also I'd like to point out that the way the stupid scroll is worded makes you believe it adds 3 stars