The problem is most likely caused by Mac user who use the Preview application to fill-in and save the form. Preview corrupts PDF forms. For more information, see: http://kb2.adobe.com/community/publishing/885/cpsid_88564.html
The solution you found is one thing you can do if you have Acrobat, but the article has something you can use with just Reader.
A simply solution is to open the offending PDF in Preview. Go to the File Menu and select Export. Under Quartz Filter choose "Black & White". Save the file and open that one in Preview and all should be good. Note: I have only tested this under Preview in Apple Mavericks 10.10.1
This will not work on a Windows system.