Sale applied to a category but it discounted almost storewide

I have a few sales on different categories running but today when I changed the percentage on an existing sale it discounted heaps of other categories along with it even though they weren't ticked in the sale maker.

I have now deleted all of my sales and doing it that hard way by individually editing each product.

What could be causing the problem as this isn't the first time it has incorrectly assigned sales to many other categories in error.

What version of Zen Cart are you using?

Clean install or an Upgrade?

Sale Maker uses the master_categories_id of a Product to determine sales ...

If you do not have Linked Products, then the master_categories_id should match the only categories_id that it is in ...

If you do have Linked Products, then the master_categories_id should belong the the Category that "owns" the Product ... meaning, that when you put a Category on sale, should the Product be on sale ...

If you import Products, you could be missing the master_categories_id as well as the products_price_sorter in the table:
products

The products_price_sorter is used for sorting Products by price, without having to calculate this price ... the products_price_sorter is the Lowest price a Product can be purchased for ...

If you do not use Linked Products, and your master_categories_id are not correct you can go to the Tools ... Store Manager ... and use the:

Reset ALL Products Master Categories ID
to be used for Linked Products and Pricing:

Then, you would want to run the Update on the Product Price Sorter:

Update ALL Products Price Sorter
to be able to sort by displayed prices: Update

If you do use Linked Products, you can still use this method, however, the master_categories_id will be set to the lowest value of categories_id found for the Product, and you may need to reset this value either individual by Product for those that are incorrect, or use the Multiple Categories Link Manager ... which you would find when you hit the C for Copy on a Product ...

Reset ALL Products in the selected Category to use the selected Category as the new Master Categories ID ...
Example: Resetting Category 22 would set ALL Products in Category 22 to use Category 22 as the Master Category ID

If you are using older versions of Zen Cart than v1.3.9, you will need to at the minimum, apply all of the Known Bug Fixes:
http://www.zen-cart.com/forum/showthread.php?t=82619

and all of the Security Patches and Updates:
http://www.zen-cart.com/forum/showthread.php?t=131115

or, upgrade to the current version of Zen Cart, on our Home page ...

NOTE: the Upgrade contains all of the Known Bug Fixes and Security Patches and Updates as well as much, much more ...