HDMI audio output disappears after re-plug HDMI cable with [AMD/ATI] Oland [Radeon HD 8570 / R7 240/340 OEM]

We have a desktop equipped with [AMD/ATI] Oland [Radeon HD 8570 / R7 240/340 OEM] card.

01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Oland [Radeon HD 8570 / R7 240/340 OEM] [1002:6611] (rev 87) (prog-if 00 [VGA controller])
	Subsystem: PC Partner Limited / Sapphire Technology Oland [Radeon HD 8570 / R7 240/340 OEM] [174b:7430]
	Flags: bus master, fast devsel, latency 0, IRQ 156
	Memory at c0000000 (64-bit, prefetchable) [size=256M]
	Memory at dfe00000 (64-bit, non-prefetchable) [size=256K]
	I/O ports at e000 [size=256]
	Expansion ROM at 000c0000 [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel driver in use: radeon
	Kernel modules: radeon, amdgpu

It has an internal speaker. If the HDMI is re-plugged, the audio output is shown as HDMI output, which is same as before. But the real audio outputs from internal speaker, instead of HDMI output. This weird state keeps until I choose internal speaker once. Then it works correctly with internal speaker & HDMI.