It's always an issue, but the force needed to move the reserve rounds changes with the number of rounds; more rounds means more force is needed but the required force will fall off as the ammunition is consumed, too much force or too little at any point and you risk the weapon jamming or the ammunition being damaged if not both at once. Keeping the capacity small minimizes the change in required force, and thus the chance that the weapon will jam, the smaller size also means that the magazines are less likely to get damaged and are easier to repair or replace when they inevitably do, which also reduces the chance of a jam occurring.
That's the answer to a different question, which is the difficulty of making it work, not whether it's bad if something goes wrong. I also don't trust the research of this manga to be that deep.