Why is mouse cursor stuck when Xbox Live shell dialogues pop up?

When my game invokes the sign-in shell dialogue for Xbox Live (on Windows 10 Store platform), the mouse pointer (cursor) appears but does not move or accept clicks. I have to Alt-Tab (or press Windows Start button) to activate mouse input. It is as if my game is still eating the mouse input, or the popped-up window is not focused. What might I be doing to cause that? It occurs in both full screen and windowed mode.

I was previously using Cursor.lockState = CursorLockMode.Confined when in full screen mode, but I commented that out, and anyway it happens in windowed mode as well in which I was setting Cursor.lockState = CursorLockMode.None.

I should have also mentioned that I’m using a custom Default Cursor in the game. I just tried not using a custom cursor (just the OS cursor instead), and that solves the problem. With the custom cursor I am also unable to move the cursor off the game screen/window, in addition to getting a frozen cursor when the Xbox Live shell windows pop up.

So I think the answer is going to be to restore the OS cursor–using a call I found in another thread: Cursor.SetCursor(null, Vector2.zero, CursorMode.Auto) )–just before invoking the pop-up windows in question, then return to my custom cursor when the game resumes control.