AX92u Internet Traffic UL/DL reversed when using USB modem (ie phone USB tether)

[Wyehoota]

Router Model Affected
Models: RT-AX92U

Firmware Version Affected
3004.388.6_2_alpha1 - prob all earlier 388's

Is this bug present in upstream Merlin releases too?
Unknown

Describe the bug
When connected to a USB modem for WAN, the traffic coming in appears as UL rather than DL. Connected to an Ethernet modem, the traffic is reported correctly.
Likely a kernel error in the USB driver ie via "ifconfig usb0" also reports traffic the wrong way around.

** To reproduce, connect to USB modem (phone in USB tether mode) and view traffic counters and/or ifconfig output.

Expected behavior
Traffic counters should be consistent independent of WAN modem used.