You have this issue on an A09, or another drive?
Well, You are right, It does seem to "work" ok despite this problem, but what concerns me more is multitasking while burning. If read-rate is affected by minor pc use, I assume write-rate will be similarly affected, with the possible help of the 2MB buffer.
What is odd is that none of the other writers I have had or have in the machine (Plex 716, Pio. A08, BenQ 1620, Liteon 167 reader) have had this issue.
As reading goes, youre right: Its adding a few seconds to the rip time - not a big deal, but if you are looking for a read curve to show some indication of burn quality, its useless with this drive. And though I haven't had any issues with the few burns (mostly tests) that I've done, moderate or esp. heavy disk I/O while burning would concern me with this drive. I would also mention that in my tests of "using the PC" while doing CDspeed transfer rate tests, one time I got a "read error" box pop up that stopped the process cold. The disc is pristine, and reads smooth to 16X on my liteon, or smooth to 12.2X on the Pioneer if you don't touch the keyboard. This worries me alot more than the jagged graph.
I have changed the auto-selected DMA mode in motherboard bios from Mode4 to Mode2 (which it also supports), but doesn't help. Seems the IDE interface on the drive is got an issue of some kind.