Bug duplication steps on Linux wallet: * open bitcoin-qt * open debug window, console * then do a 'importprivkey' command, * then do a 'walletpassphrase' command, * back to the main window, and open the 'Receiving addresses...', * change the label for that imported address * and the ui blocked
refer to the commit aefbf6e30cadaf77ebee44284c74cc5449dc173f
After importprivkey, did you wait for the operation to complete? It is a lengthy operation (can take >10 minutes on mainnet) rescanning the blockchain for usage of that key and the client may not respond in that time.
It will respond again after the rescan is complete.
If you don't need a rescan (when you're sure that the key is never used on the block chain) you can provide false for the rescan argument of importprivkey.