I just updated to 3.5 and ran a backup and got this
1. try to create backup zip (PclZip) archive...
2012/12/22 15:40.11: [ERROR] Job restarted, because inactivity!
2012/12/22 15:40.11: 2. try to create backup zip (PclZip) archive...
2012/12/22 15:49.38: [ERROR] Zip archive create error: PCLZIP_ERR_MISSING_FILE (-4) : File '/xxx/yyy/public_html/kids/wp-content/w3tc/objectcache/0/0/0/000eabc5642d19318c5b45eb7c359e4e' does not exist
2012/12/22 15:49.38: [WARNING] filesize(): stat failed for /xxx/yyy/public_html/kids/wp-backup/backwpup_1_2012-12-22_15-25-41.zip
2012/12/22 15:49.38: Job done in 1437 sec.
Worked like a charm before 3.5