I'm no expert on HP switches, but sounds to me like they something wrong in their software.
Might be worth an upgrade if one is available.
Also open up a support ticket with HP as it's something they should probably be told about
This has happened through FIVE (5!) software revisions, we have opened up 2 separate support tickets with HP, both of which they state they cannot duplicate our issue... This posting was a last gasp effort to see if we could find another solution.
Our work-around is to run the SNMP Sweep in very small increments (one subnet at a time!), and excluding our HP 5308 switch IP's from this discovery. It works, but is tedious...