Random things happening

I have noticed some random, non-reproducible things happening since the last major update. The most bizarre was a tile of refined carbon (!) suddenly appearing over a valve, but I have seen others. Not very frequent, but they keep happening. I suspect there is some rare conditions were a tile descriptor gets corrupted in some fashion, e.g. by having the wrong data-type copied to it or something like it. I did not notice anything like that before the "fast friends" update.