The one-click Steam key redemption feature will no longer be available from Humble Bundle on purchases made after 12th January 2015.
The announcement was made via the Humble Bundle blog yesterday. It said that the 'OAuth' Steam key redemption system they implemented just over a year ago was no longer being supported by Steam.
This means that the old manual system is back, so, you will have to copy and paste your Humble Bundle Steam keys into Steam's "Activate a Product on Steam" feature to redeem your purchases.
It is a minor inconvenience to have to manually input the keys, but what about those huge Humble Bundle deals with many games - how will we cope?