I've been placing apiaries today and every 2-3, the game crashes out to the 'Downloading terrain' screen. Nothing happens after that until I quit the game. It's happened a number of times now. Doesn't seem to matter whether I place the apiaries from the stack or separate them first.
I created a ticket for this and other Forestry machine-related issues. It should be fixed; SirWill created a patch for it. I believe the Downloading Terrain screen is an attempt to transition you back to the hub that failed. You can get out of it without restarting your client simply by turning your WiFi off or disconnecting your Ethernet cable, which will cause the connection to time out and return you to the Minecraft home screen.
