I've tested that several times with different games. To reproduce the issue:

• Spec into Fiery Blast (Reflexes > Blades)
• Equip a melee weapon and check it's stats (dps & aps)
• Use it in combat; it may take some several kills/attacks
• Check the stats of your melee weapon

The dps & aps will reduce and eventually hit zero. Same for blunt weapons when you spec Payback (Body > Street Brawler). Workaround: Drop the weapon and pick it up again. For Mantis Blades/Gorilla...

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