Hello from 7 years later! I was having the same issue and figured out a janky workaround. Right-clicking to add a node seems to disable the ability to enter text in the search bar, but dragging from another node to initiate the contextual search will retain your ability to type in the search bar. If you select an object in your scene, then right-clicking in the graph editor will show the selected object near the top of the list, then you can drag from the node relating to that object. You can disable “Context Sensitive” if that object is unrelated to anything you want to do.