Zero shouldn't be an option.
I have used scroll binder to bind alchemy pink scrolls up to 5 and at the end i got scammed :p It gets even more interesting because i made a proper one +5 alchemy SoT just a moment before. Maybe it's the order in which the scrolls are added. I also noticed math going crazy sometimes when you...
trueuo.com
I'm going to guess somewhere in the code that creates these things also needs a tolerance level set. So, yes a rounding error sounds spot on.
You said it came from a treasure map chest?