Don't know if this is a bug, but it doesn't seem to happen with other resources.
When harvesting materials in this game if I have any organic matter on the back of my terraforming gun I will not be able to harvest any other materials. The only way I can resolve this is if I, as carefully as possible, harvest organic matter until I make a solid block of organic and not a single drop more. This also gets especially irritating if I'm trying to harvest a different resource that happens to be near organic and pick up the organic by accident.
I play with k+m on Steam, Windows 10, Nvidia GTX 770 with an Intel i7 series CPU.