If you (accidentally or on purpose) double-tap ammo pack ability button (in my case it’s default “X”) and keep it pressed on second tap, most of the time animation gets stuck to infinite loop, but no ammo is thrown out. You can reproduce that at any time when having something like two ammo packs available. This is also happening to Sawbonez medpacks (by pressing double “C”) and I guess it works with Sparks’s and Arty’s med/ammo packs also. Small video example how it looks.
Skyhammer:
Sawbonez: