In 0.12, a wallet tx thats not in the mempool does not free up its inputs.  So if a tx spends the same inputs as a conflict tx included in a new block, its inputs are explicitly marked dirty so they will be recalculated as spendable again due to having no non-conflicted spends.  However if the in-block conflict is reorged out, the wallet txs inputs should now be market spent again according to the 0.12 regime, but they are not marked dirty as the tx itself is not notified it is no longer conflicted.

This has the odd effect that the cached value is incorrect and so randomly they will be spendable or not depending on whether they have been recalculated.

This is easy enough to fix by marking all inputs of all txs in SyncTransaction dirty regardless of whether AddToWalletIfInvolvingMe returns true or false.  But I'm not sure the performance impact this will have, so I'm not proposing that change now.

It's a minor issue, but I just thought I'd document that that the cached credit available in wallet txs may not always be correct.

For reference, in 0.11, whenever a tx left the mempool it's inputs were respendable.  So if a tx was removed due to a conflict in a block, any remaining inputs would be spendable again.  If the in-block conflict was later reorged out, the wallet txs inputs would remain spendable unless and until the wallet tx reentered the mempool.

for (const auto& entry  mapKeyFirstBlock) {
        int64_t block_time;
        CHECK_NONFATAL(chain().findBlock(entry.second->confirmed_block_hash, FoundBlock().time(block_time)));
        mapKeyBirth[entry.first] = block_time - TIMESTAMP_WINDOW; // block times can be 2h off
    }
}
/**
 * Compute smart timestamp for a transaction being added to th.
 *
 * Logic
 * -  sending a transaction, assign its timestamp to the current time.
 * -  receiving a transaction outside a block, assign its timestamp to the
 *   current time.
 * -  receiving a transaction during a rescanning process, assign all its
 *   (not already known) transactions' timestamps to the block time.
 * -  receiving a block with a future timestamp, assign all its (not already
 *   known) transactions' timestamps to the current time.
 * -  receiving a block with a past timestamp, before the most recent known
 *   transaction (that we care about), assign all its (not already known)
 *   transactions' timestamps to the same timestamp as that most-recent-known
 *   transaction.
 * -  receiving a block with a past timestamp, but after the most recent known
 *   transaction, assign all its (not already known) transactions' timestamps to
 *   the block time.
 *
 * For more information see CWalTxnTimeSmart,
 * https//bitcointalk.org/?topic=54527, or
 * https//github.com/bitcoin/bitcoin/pull/1393.
 */
unsigned int CWalComputeTimeSmart(const CWalTx& wtx, bool rescanning_old_block) const