It's not really a bug, but it's useful^^
Change your job to a merchant/Blacksmith and Enhance the skill "Increase Weight Limit" to lvl 8.
Now you can carry an item 99 times (not equipment). Buy berrys, Potions or whatever 99 time and rebirth.
Now you have 99 red potions and other stuff in your inventory without having this skill^^
But if your items are gone, you can only buy 20 again.