I have the same problem and the problem is not S2-tuners. I have T tuners and i also get this problem when i record on one channel and change channels in the meantime. When i then play up the record i get dropouts and i can refer it to channelchange. I flashed my dm8k a couple of days ago and i used to use Gemini2 v5.10 with no record problems at all. I have not played around with the sleep settings on the HDD. I use 20121020 image.
Have you got any solutions on this? Everything else on the image works great, i now use a T2 usb tuner, the EPG data is very good, I really like it!