I seem to regularly get 'cloudy' burnt dvds, they start fine, but then half way through the write surface is this white cloudy area - obviously the disks don't work, but why is it happening?

Media type isn't an issue, it happens on all that I've tried and I've set up a 98se partition with no non-essential processes just for DVD burning.

Programs aren't an issue either, it happens with Nero, Prassi, InstantDVD (VOB) and CopytoDVD

I'm using a Pioneer 105 with the 1.21 firmware update