It happened to me today again.. only once though.. But.. I am unable to do a video recording.. somehow my dxtory wasnt working when I tried to do the recording with it.. So I gave up.. But basically here's how I think you can try to replicate this bug/issue:
1. Equip the bullets/shells onto the ammo slot (put like 10 for testing purpose).. And make sure you have another stack of bullets/shells in the inventory on the 1st row
2. then go and kill some mobs until the bullets/shells in the ammo becomes empty and *from my understanding* it will auto equip the next available stack of bullets/shells into the ammo slot.. and ingame sound of equip ammo can be heard.. Now.. most of the time this works like a charm.. that is, you will have the new stack of bullets/shells in the ammo slot and we can continue kiling mobs as we like..BUT.. this is where the bug begins I believe, today the sound can be heard.. and I thought it auto equipped the bullets/shells into the ammo slot.. but no.. my character wasnt shooting anymore just standing there.. So I open up inventory and found that the ammo slot is empty.. So I manually double click one of the bullet/shell stack, and the equip bullet/shell sound can be heard but it disappears.. then I try on another stack, again, equip sound can be heard but the stack disappears and didn't appear on the ammo slot..
3. Next what I did was I logged out, closed the game.. login and enter the game.. then I try to equip the shells into the ammo slot, and this time.. it appears.. then I unequip it from the ammo slot, and now, a duplicate set of shell stacks appear.. I believe its not really duplicate, its just giving back the shell stacks that I "thought" i lost before i restarted the rose client? then i kept repeating this, equip/unequip into ammo slot and those shells that were lost, came back to me in my inventory as "duplicates".. well not really duplicates i supposed.. but it is a Bug you guys need to fix I think
I hope this can help you guys.. if not, if it happens again ill just have to relog and do that.. it is a hassle but i guess it can't be helped.. whats worst is if this happens during a dungeon run or CD run where My ammo disappears and the only way i can fix it is by restarting.. that would suck big time