Recent Changes to 4x DVD+R media? Speed problems

I was wondering if anyone knows of recent changes to DVD+R media.
For the last year I have been using memorex 4x +R discs with no problems and all of a sudden My last several batches of Memorex and Kodak 4X are only being detected at 2x speed. A firmware upgrade helped this but caused other problems and had to be changed back, so what did they change about the discs?