I've found a bug by a mistake. Here is the instruction to recreate this effect:
1. Be a fieldop.
2. Find a dead body of a medic from your team.
3. Throw an ammopack near this body.
4. Dress as this medic (class switch).
5. Pickup ammopack.
6. On button 5 you will have medipacks AND ammopacks.
Here is the proof:
UPDATE: It works with every class when switching from fieldop (ammopacks available on button 5). It doesn't work when switching from medic to any other class (no medipacks on button 5).
Edited by Dzikus, 20 May 2015 - 04:38 PM.