Surface Pen "Magic" button not detected

Pressing the "Magic" (eraser) button on the back of the surface pen is not correctly detected.

• When clicking the button by physically pressing it against the screen, it is correctly detected as an F20+MetaModifier key event.
• When holding the pen away from the screen and pressing the button it is only registered as a Meta key event.

The same thing seems to happen with the double-press (F19+MetaModifier) and long-press (F18+MetaModifier) events.