CD/RW Capacity Problems

As a user of Quicken, I habitually backup my quicken data file from quicken to CD and then use the windows cd writing wizard to write the files to cd. Now the odd thing is this. Each time I write the files (they are the same files each time) to the cd, the capacity of the cd is reduced by the size of the files being written, though the size used is still about the same as it was before. So, I suspect that the CD writing process is not writing over the files that existed before, but rathre creating new copies and then hiding the old files (even though the file names are the same). The annoying thing is that eventually, I have to wipe the cd clean and start over again becuse the cd thinks it hasn't any capacity remaining, even though the size of the files are only 30 mb, or so. After I erase the cd it goes back to reporting an available size of 780 mb, or so. Anyone have any ideas about this. I susupect that it is a driver/firmware problem, but would hope reading this has experienced the same situation and has a fix. The CD I am using is a Lite-On DVD RW SOHW 1633-s. I am running XP SP2 fully up to date.
Thanks,

Dan