FOSS gamedev and creative worlds

Another problem I just stumbled upon:

In desert plains on my freshly updated server I see areas of sand which are drawn as if they were "falling" and like falling sand they can not be digged or build upon, but they are not moving as they are already on the ground.

Sometimes it is possible by placing blocks next to this "pseudo falling sand" to trigger it so that it settles on the ground (which means, it stays where it is but stops "falling").

FWIW: after logging out and in again, standing next to such an area of "pseudo falling sand" the sand disappeared all together. (after logging in again it was simply gone)