When opening & using both the Timeline & Animation Windows in a certain order, hotkeys no longer respond/work.

Repro:
- Open project and close Animation Window.
Note: It is important that you have the Timeline window open, but not the Animation window.
- Close project, and re-open it.
- Open Cube scene
- Open Timeline window
- Use hotkeys to navigate time in the Timeline window (play, next/previous key, start/end)
Note: hotkeys work as expected.
- Disable Timeline preview (button)
- Open Animation Window and enable preview
- Use hotkeys to navigate time in the Animation Window (play, next/previous key, start/end)
Note: hotkeys work as expected.
- Disable Animation Window preview (button)
- Open Timeline Window and enable preview
- Use hotkeys to navigate time in the Timeline Window…
Bug: Hotkeys no longer respond/work and get the following notifications in the Console…
———
Shortcut conflict detected for key binding Space.
Please resolve the conflict by rebinding one or more of the following shortcuts:
Timeline/Play (Space)
Animation/Play Animation (Space)

UnityEditor.EditorApplication:Internal_CallGlobalEventHandler()
———
… same notification for all play control hotkeys…
Shortcut conflict detected for key binding Comma.
Shortcut conflict detected for key binding Period.
Shortcut conflict detected for key binding ⇧Comma.
Shortcut conflict detected for key binding ⇧Period.
…etc.
———
Expected result: hotkeys work as expected, no hotkey conflicts.

Repro in…
Version 2018.3.0a7 (a7130d85cac7)
Branch: trunk

Also repro in a6, but hotkeys simply do not work at all and an error is generated in the Console.
Version 2018.3.0a6 (33e5def6e55f)
Branch: trunk

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Timeline.Shortcuts.SendEventToInvokeShortcut (System.String timelineShortcutId, System.Object context) (at /Users/builduser/buildslave/unity/build/Extensions/Timeline/Editor/Shortcuts.cs:272)
UnityEditor.Timeline.Shortcuts+Timeline.NextFrame (UnityEditor.ShortcutManagement.ShortcutArguments args) (at /Users/builduser/buildslave/unity/build/Extensions/Timeline/Editor/Shortcuts.cs:99)
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <d8f4518f0e5b4dbe99711ff1e07789b8>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <d8f4518f0e5b4dbe99711ff1e07789b8>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at <d8f4518f0e5b4dbe99711ff1e07789b8>:0)
UnityEditor.ShortcutManagement.ShortcutAttribute+<CreateShortcutEntry>c__AnonStorey0.<>m__1 (UnityEditor.ShortcutManagement.ShortcutArguments shortcutArgs) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutAttribute.cs:60)
UnityEditor.ShortcutManagement.Trigger.HandleKeyEvent (UnityEngine.Event evt, UnityEditor.ShortcutManagement.IContextManager contextManager) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/Trigger.cs:94)
UnityEditor.ShortcutManagement.ShortcutController.HandleKeyEvent (UnityEngine.Event evt) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutController.cs:61)
UnityEditor.ShortcutManagement.ShortcutIntegration.EventHandler () (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutController.cs:23)
UnityEditor.EditorApplication.Internal_CallGlobalEventHandler () (at /Users/builduser/buildslave/unity/build/Editor/Mono/EditorApplication.cs:318)

Not repro in…
Version 2018.3.0a5 (20706b925e3c)
Branch: trunk