I've been waiting around 5 hours.
https://blockchain.info/tx/9b1bced645d138443cbc18dbd7002612cc54976ccb612d2d94a6aec4c826397a

Thanks for the reassuring responses 
I don't pretend to quite understand what has happened here, but it's good to know that it's apparently a recognized issue.
Could someone offer a brief, noob-friendly outline as to why a84fbe6372584f39363e01902e96e4e67858c6c9e8a6cfe511c0a7df8f198420 (not my wallet) is unconfirmed and how I can avoid this happening again? Not terribly comfortable with the notion that I can spend bitcoins and have them confirmed in minutes not hours, but only conditionally, depending on the way in which they were sent to me.

Is anyone able to tell me what I've done wrong here? I've been waiting hours for confirmations but apparently it's not happening anytime soon. Isn't filing me with faith that I should persevere with bitcoin. 

9b1bced645d138443cbc18dbd7002612cc54976ccb612d2d94a6aec4c826397a