>
> SPV wallets can't detect hard-forks


They don't have to - they pick the highest work chain. Any miner who hasn't
upgraded makes blocks on the shorter chain that are then ignored (or
rather, stored for future reorgs). After the fork point, there won't be any
blocks in the main chain that violate the rules and end up being doomed to
being orphaned, which is the underlying problem.

And I think you know this already. There is no "flaw" in bitcoinj in this
respect. It works exactly as it was designed to work.