small rectangle at mouse pointer?

Widelands 6549

Graphic Bug report:
There is a funny little square (I guess it's 3x3 Pixels)
a bit below the mouse pointer that I have not seen before.
It moves together with the pointer, but is only visible
when you point straight at a house and the yellow Maltese cross shows.

I wonder whether this is a bug... it's quite handy in fact
marking the correct spot to invoke the building's window.
But in that case it should be red or orange to better show on all terrain types.