Make sure that when you delete a keyword, you do it everywhere.

There are several reasons you may decide to delete a keyword. It could have proven to be an ineffective keyword based on PPC campaign performance, it might be disabled, or you just may want to move the keyword elsewhere. If you need to delete a keyword, you must take care to delete every instance of the keyword in your ad account! To make sure you accomplish this, search each of your ad groups – including deleted groups - for this keyword. If you find the keyword, edit the keyword list and remove the keyword, and be sure to save the changes.