It sounds to me as if Symantec have answered your question. If I read what you have said and what they have replied correctly, then access is denied to some of the reports to other users but some reports are available to anyone and can be deleted.
If I read this right then that is the way they have designed the program. Therefore its working correctly. Why they would design the program so any user can delete some of the reports I don't know. I would have thought it would have been better to make the administrator the only one who can delete any reports. But obviously they think differently.
If I've picked up your meaning correctly you are stuck with it. The only solution I can see is if Symantec change their mind about the way the program works and decide to update it but I think thats unlikely. They might take your issue on board and alter the next version so that the only one who can delete reports is the administrator or they might not. Its really up to them.