I had this problem too
In Exchange System Manager, Right click the Server and go into Properties, UNtick Remove Log files. I had this set to remove log files after 2 days (don't do this)
Assuming doing a full backup each night, Inside veritas on the Exchange Tab of the backup job make sure its says "FULL flush commited logs"
I think what was happaning was Vertias was trying to flush the logs but exchange was saying it wanted to keep the logs for 2 days.
I was getting up to 2gb's of extra logs
I didn't explain it very well but mail me back if you still have probs.