I guess the reason is that I changed the trackers to manipulate the "reference offset" instead of the "reference". See "collateral changes" in #127.

Ideally the head in the GUI should show both pieces of information, but I'm not sure how this can be achieved.

For loudspeaker-based renderers, there is a little cross symbol that shows the reference offset.

Ah, yes, that might be it!
I agree with the change. Even if listeners turn their head, the scene coordinate system stays the same.
But in this case the GUI Head should reflect the "reference offset"!

BTW, there is also a little cross on top of the GUI head. So maybe it is even possible to show both?

This cross marks the origin of the global coordinate system. It is not movable.

In qopenglplotter.cpp, there is an if/else statement:

if (_plot_listener)
{ 
    (...)
}
else
{
    (...)
    // draw cross (showing the reference offset)
    (...)
}

This would needed to be changed (it's here) for the reference offset also to be visible when a listener is apparent.

I think this has been fixed in #358 and #360.

I think this has been fixed in #358 and #360.

The latest release indeed fixed such an issue with a Polhemus tracker for me.

Closing since seems to be fixed in the meantime.