Hi
I have the same problem with my iMac, in which resides a different drive model than yours:
"*PIONEER DVD-RW DVR-K06A*:
+Firmware Revision: Q631+
+Interconnect: ATAPI+
+Burn Support: Yes (Apple Shipping Drive)+
+Cache: 2000 KB+
+Reads DVD: Yes+
+CD-Write: -R, -RW+
+DVD-Write: -R, -R DL, -RW, +R, +R DL,
RW
+Write Strategies: CD-TAO, CD-SAO, CD-Raw, DVD-DAO+
+Media: Insert media and refresh to show available burn speeds+"
If you search in Google my drive's model you will find much more problems though …
So, it might be a relief to you what I'm saying, since you (lucky ones!) are just … skipping a "damaged area" of your DVDs and likely, the next moment you continue to watch you movies!