I posted this on apple discussions , but not really resolved, any one else got this problem
I have two computers running 10.6.2, both backing up to a Western Digital World Book 1TB, running the latest firmware, using Time Machine.
This device supports Time Machine according to WD's web page.
One computer, within 24 hours of the initial backup, starts to backup large amounts of files, approx. 80Gb.
There is no way that I have made these amounts of changes, all prior backups are what I regard as typical
for the work I do, max 300Mb.
Excludes on this machine appear to be ignored.
The other computer backs up correctly.
Also, using an USB disk on the machine that makes big backups, the problem is not there, so its
one machine using the network drive, that has this problem.