Custom Activities not showing in VS2012 Toolbox

Situation: I created a Windows Workflow Foundation (WF) application using custom Workflow activities. I compiled the project and found out that my toolbox are not showing the custom workflow activities despite re-building, re-adding the reference to the project.

This is how it looks like in my solution.

See ma! No custom workflow activities!
Look ma! No custom workflow activities!

Gandalf: Thou shall not pass!

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