Looked a bit closer at my backup logs:
16/10/12 4:08:26.124 PM com.apple.backupd[34806]: Backing up to: /Volumes/Time Machine VadeMACumPro2/Backups.backupdb
16/10/12 4:08:41.209 PM com.apple.backupd[34806]: Using file event preflight for Macintosh HD
16/10/12 4:08:41.304 PM com.apple.backupd[34806]: Will copy (60.2 MB) from Macintosh HD
16/10/12 4:08:41.306 PM com.apple.backupd[34806]: Found 76 files (60.2 MB) needing backup
16/10/12 4:08:41.312 PM com.apple.backupd[34806]: 8.06 GB required (including padding), 1.13 TB available
16/10/12 4:26:07.765 PM com.apple.backupd[34806]: Copied 3795 files (23.96 GB) from volume Macintosh HD.
hmm. 60.2MB needing backup, .06GB required, 23.96GB copied???
16/10/12 4:26:08.262 PM com.apple.backupd[34806]: Using file event preflight for Macintosh HD
16/10/12 4:26:08.991 PM com.apple.backupd[34806]: Will copy (14.3 MB) from Macintosh HD
16/10/12 4:26:08.992 PM com.apple.backupd[34806]: Found 44 files (14.3 MB) needing backup
16/10/12 4:26:08.993 PM com.apple.backupd[34806]: 10.38 GB required (including padding), 1.11 TB available
16/10/12 4:28:26.972 PM com.apple.backupd[34806]: Copied 1553 files (2.22 GB) from volume Macintosh HD.
16/10/12 4:28:28.399 PM com.apple.backupd[34806]: Created new backup: 2012-10-16-162827
16/10/12 4:28:34.404 PM com.apple.backupd[34806]: Starting post-backup thinning
16/10/12 4:28:34.404 PM com.apple.backupd[34806]: No post-back up thinning needed: no expired backups exist
16/10/12 4:28:34.726 PM com.apple.backupd[34806]: Backup completed successfully.
so that finished after it had sais 14.3MB need backp, but 10.38GB required and then it copied 2.22GB...
and then:
16/10/12 5:08:25.463 PM com.apple.backupd[37537]: Starting automatic backup
16/10/12 5:08:26.083 PM com.apple.backupd[37537]: Backing up to: /Volumes/Time Machine VadeMACumPro2/Backups.backupdb
16/10/12 5:08:27.815 PM com.apple.backupd[37537]: Using file event preflight for Macintosh HD
16/10/12 5:08:28.272 PM com.apple.backupd[37537]: Will copy (667.7 MB) from Macintosh HD
16/10/12 5:08:28.274 PM com.apple.backupd[37537]: Found 86 files (667.7 MB) needing backup
16/10/12 5:08:28.281 PM com.apple.backupd[37537]: 8.76 GB required (including padding), 1.13 TB available
and now it's at 17 of 18GB (when it said 8.76GB needed) (but only 667.7MB needing backup??)