This is a question we see pretty regularly, and normally there are a few things to look at in answering.
First, a high number of discards means an upstream/downstream interface combination of different speeds is forcing one side to discard packets due to load at various times. If you begin to see the error counters increase as well it means you have sufficient load that it is over-loading not only the interface logical ability to process packets, but also the physical capacity for processing data is failing resulting in errors. While a small number of discards is pretty normal, ensuring you have sufficient bandwidth to avoid both of these conditions is important.
As for the traffic utilization, it is not uncommon for a fractional interface to burst above the committed traffic rate. This can be seen on both fractional T1 and fractional DS3 interfaces fairly often.
Most of the time these bursts account for excess traffic being reported.
Ocassionally it is also possible that the device/interface simply hits an error in updating the counters. This is far more likely to occur on a device experiencing high sustained loads.
An important note to remember of Orion reporting in general is that we can only deliver graphs and reports that are as accurate as the information we collect. Unforturnately it's not uncommon that devices sometimes provide bad data.
Hope this helps.