[Bug] OSM SHIFT sometimes behaves incorrectly (oryx, moonlander) (RDP related)

One of thumb keys on my Moonlander is configured as one shot shift modifier (and nothing else). Occasionally it doesn't produce shifted next letter but regular lowercase letter. The problem is not in timing. This happens when the osm shift key is pressed and released withing the tapping term so should produce shifted character.

I created simple debugging app that prints keyUp and keyDown events and prints them with timestamp (second.milliseconds). On screenshot below you can see that few times osm shift worked as expected, but then one time it produced lower character because keyboard sent:

shift down
shift up
X down
shift up
X up

The first shift up seems like bug?

System Information

• Keyboard:
  Moonlander mk I, configured with oryx online, flashed with Wally, my tapping term is set to 300 ms so this is not caused by holding the shift too long on the contraty this seems to happen when I press the button very swiftly

• Operating system: Windows 10

• Any keyboard related software installed? No