When do you need to run bitcoin-qt -rescan? I was under the impression that the -rescan flag was no longer needed for some time now. Can someone document precisely, when does one need to run bitcoin-qt -rescan? How has this changed throughout the versions of bitcoin-qt?
This answer might help: https://bitcoin.stackexchange.com/a/1251/11026

The gist is that a -rescan was needed, when you were restoring an older backed up wallet that didn't have all the transactions in your current blockchain reflected. Basically the client then goes through your blockchain to see if there are any transactions that affect your wallet.

However, you don't have to worry about this anymore since the client now checks automatically if the wallet is on the same level as the currently downloaded blockchain, and if needed, does the rescan:

https://bitcointalk.org/index.php?topic=6642.msg99812#msg99812

Hope this helps.