GitHub: https://github.com/Unity-Technologies/InputSystem/issues/472
https://github.com/Unity-Technologies/InputSystem/issues/538

Repro:
1. Download attached asset package "EnableTest"
2. Download package and project at: https://github.com/Unity-Technologies/InputSystem
3. Use existing scene or create a new one, import the asset package into the project
4. Attach the C# script "EnableEventTest" to any gameobject, then attach InputAction, "TestControls", to the script
5. Enter Play Mode
6. Press 1 on keyboard, and some messages appear in the Console
7. Press 2, and the Action for 1 is disabled. Press 2 again to re-enable the 1 Action.
8. Press 1 now

Actual: The callback function bond to Input Action is lost after the Action is disabled and re-enabled again.

Note: In the C# script "EnableEventTest", "OnSecondPerformed" function, un-comment the three lines of code. This will rebind the callback functions to the first action before it is re-enabled. But they still won't be fired.