Code based interfaces do not appear in Interface selection dropdown

When adding an interface to a blueprint, only blueprint created interfaces are available. Engine / custom interfaces written in code are not listed.

Regression:
Yes - custom interfaces are present in 4.15.2
Working 4.15.2 (CL 3416026)
Broken 4.16 Preview 2 (CL 3415565)

1. Open UE4 Editor (any project)
2. Create blueprint Based on Actor
3. Click Class Settings button in the toolbar
4. Click the Add Dropdown in the interface section of the Details Panel

Result:
Tutorial_BP_Interface is the only available interface to add

Expected:
Engine interfaces are listed and can be added to the blueprint

C++ Blueprintable Interface issue