The websocket notification server will deregister websocket clients from receiving notifications for a transaction when the spending transaction is in a newly attached block. The purpose of this is to prevent ramping up memory usage for tracking outputs that can not be spent again. However, during reorg, if the block containing this transaction is removed and the transaction also is included in the new best chain, a websocket client may not be notified of the transaction because the watched output is no longer watched. This can cause websocket clients (e.g. btcwallet) from believing that some spent outputs are still unspent.