QuickBooks has no native fund accounting, so the separation between operating and reserve is constructed on top of it — usually through class tracking — and the software will not stop anyone breaking it.
The practical consequence is that an association's books are only as good as the tagging discipline behind them. Every transaction has to carry its fund, and nothing in the software complains when one does not — a reserve expense posted without its class simply lands in operating and the two balances quietly stop meaning what they say. That is why associations that have run for years without a bookkeeper who understood the structure usually need a rebuild rather than a correction: the drift is not one wrong entry but a slow blending. Turning class tracking on properly is the mechanical part, covered on our class tracking setup page; deciding what the classes must be, and holding the line afterwards, is the part that needs someone who knows what an association is.