Good question...
I don't have a good answer because I thought that all the Monarchs were manufactured to the same standards. You seem to have thought that also.
Simply, a monarch is a monarch is a monarch...evidently not!
Nonetheless, drop PM an email for their input.
Also, when you order cards, an 'old, sage magicman' once told me to always order cards from one trusted supplier.
I never gave it much thought until now ;-)
Maybe you got an 'older' edition red, and a 'newer' edition green.
They have them both here at PM.
http://www.penguinmagic.com/search.php?q=monarch+deck