Users should be aware of new behavior in Zcash that differs significantly from Bitcoin: in the case of a block chain reorganization, Bitcoin's coinbase maturity rule helps ensure that any reorg shorter than the maturity interval will not invalidate any of the rolled-back transactions. Zcash keeps Bitcoin's 100 block maturity lapse for generation transactions, but because JoinSplits must be anchored within a block, the protections this provides are much more limited in scope. In the case of a block chain reorg for Zcash, all JoinSplits which were anchored within the reorg interval and any transactions that depend on them will become invalid, rolling back transactions and reverting funds to the original owner. The transaction rebroadcast mechanism inherited from Bitcoin will not successfully rebroadcast transactions depending on invalidated JoinSplits if the anchor needs to change. The creator of an invalidated JoinSplit, as well as the creators of all transactions dependent on it, must rebroadcast the transactions themselves.
Receivers of funds from a JoinSplit can mitigate the risk of relying on funds received from transactions that may be rolled back by using a higher minconf (minimum number of confirmations).