Key Binding Vertical speed issue

Hi all,
has anybody else experienced that it´s not possible to assign a key to Vertical Speed button?
I can inc/dec the altitude, but changing VS level only works when I click the buttons with the mouse.
When I assign any buttons to “increase autopilot reference vs”, nothing happens.

Is it a bug or am I doing something wrong?

Same problem here.

When i click up or down with the mouse first then my VS up and down bind on my hotas are working