Obstructive, Invincible Falling Sand

On Multiple occasions now i've had instances where i've dug out materials from below sand and had singular sand blocks seemingly fall in place, immobile and indestructible, my duplicants will try and remove the sand from the designated location that it is supposed to fall but as it's not fallen they are unable to remove it and the sand obstructs and building in its fall radius or on the initial block where it's falling in place. 

Anyone else experiencing this issue? It also seems to slow down performance.