Reproduction steps:
1. Open attached project "1217379_input_system" and make sure "Input System Package (New)" is selected in Edit > Project Settings > Player > Active Input Handling
2. In the Project window, double-click on "1217379_input_system" Input Action file to open the Action editor
3. In the top left corner press "All Control Schemes" and "Add Control Scheme..."
4. Set the Scheme Name to "All Control Schemes" and press Save
5. In the top left corner press "All Control Schemes" again

Expected result: Created Control Scheme can be selected in the dropdown list
Actual result: Created Control Scheme can't be seen in the dropdown list

Reproducible with: 2018.4.17f1, 2019.3.2f1, 2020.1.0a23
Could not test with: 2017.4.37f1 (no Package Manager)

Reproducible with package versions: 0.2.1-preview, 1.0.0-preview.4

Note:
When creating a Contol Scheme with an identical name to the other selections in the dropdown (XR, Gamepad, ...) a number is added to the end of the new Control Scheme (XR1, Gamepad1, ...) and it can be seen in the dropdown list

With 0.2.1-preview reproducible when using "No Control Scheme" instead of "All Control Schemes"