I agree that the behavior should be specified. It would seem that this is an opportunity to take advantage of Diameter's M-bit in governing the gateway's behavior.
In theory the Diameter/RADIUS gateway could discard Diameter AVPs without the 'M' bit set in order to fit within the RADIUS packet size limit. However if there are multiple attributes of a given type, it might not be appropriate to discard some but not all of them. So in practice, the rules might get quite complex. If we believe that this is a problem which is only likely to occur due to mis-configuraiton, then it might be better for the gateway just to indicate that a problem has occurred to the source and destination and leave it at that.
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