What's the Deal with "Do Not Double" on certain coupons?

Have you ever noticed the dreaded "Do Not Double" on a coupon and been worried about it?  I live in a great area I have a Meijer that doubles coupons up to $.50 as well as several local grocery stores.  I have a VGs that doubles coupons up to $1.00 and I work near a Kroger that doubles coupons up to $1.00.  So when I have a plethora of coupons that say "Do Not Double" what does that really mean?  There are actually a two groups that these break down into.  The first group are the coupons that are readily accessible and the bar code starts with a 9.  These are usually the tearpads, blinkies and some home mailers.  They are coded to not double because the manufacturer knows they have a higher redemption rate.  Any barcode that starts with a 5 will double automatically when scanned.  So why are some coupons that will double automatically worded with Do Not Double? Well I have read a few articles and heard it discussed and here is the deal.  When a store offers double coupons that is an additional Store incentive.  When this first occurred some stores wanted to solicit the full amount from the manufacturer which manufacturer's did not authorize.  So to make it clear that to stores they will only be reimbursed the face value of the coupon they put "Do Not Double" on certain coupons. 
The stores are taking a hit on these coupons and using them like they do their "loss leaders" to get you to come to their store rather than a lower priced store. 
So what about the Do Not Double coupons that start with a 5?  Basically two things are involved, the coupon policy and the cashier.  If the coupon policy states that all coupons are doubled to a certain amount then they should be doubled.  Some coupon polices do state that all coupons (of a certain value) will be doubled unless the coupon states otherwise.  (For example check out Busch's Coupon Policy.)  Then there are the cashiers who not knowing the intent of the "Do Not Double" will restrict your coupon. 
So basically know your coupon policy and the cashiers and act accordingly.  If the coupon policy states that all coupons to a certain amount are doubled but the cashiers restrict them often at that store perhaps speak with the manager.  (But proceed with caution because the end result could be changing the wording of the coupon policy.)  You may also want to opt for the U-scan or take your business else where.  You can find more in depth information at these two articles  here and  here.