"Mapped port" input discarded while corresponding controller is disconnected

Description

Given two controllers connected with the "dinput" input driver and "xinput" controller driver, both mapped to core port 1, when the primary controller (player 1) is disconnected, the secondary controller (player 2) is no longer functional until primary is reconnected. RetroArch confirms via OSD that secondary has been remapped as controller 1, but core receives no input data for port 1 until the original controller 1 is reconnected.

Using the dinput controller driver instead of xinput produces the expected result but precludes usage of the Guide button for RetroArch hotkeys, so I'm filing this issue to petition for a solution on xinput's side.

Expected behavior

With two controllers mapped to port 1, each should continue controlling port 1 even if the other is disconnected.

Actual behavior

Secondary controller no longer controls port 1 when primary controller is disconnected.

Steps to reproduce the bug

1. Set dinput input driver and xinput controller driver
2. Set player 2's "mapped port" to 1
3. Turn on two controllers
4. Launch a game
5. Disconnect the controller that was connected first
6. Observe that the controller connected second no longer works

Version/Commit

• RetroArch: v1.9.7 (official)

Environment information

• OS: Windows 10 Pro x64 20H1

Start by reproducing the disconnect and remapping sequence on Windows with the dinput input driver and xinput controller driver. Read the xinput controller-driver handling around controller disconnects and mapped ports, then verify that the remaining controller still delivers input to port 1 after the original controller is removed.