Decay?

Does some stuff just decay when built off a claim?
So far, one of my drying racks disappeared. No biggie, but when it disappeared I had heaps of stuff lying around so it didn't strike me as likely that someone took it.
More distressing: tonight my ore smelter is gone.
And yet, I often see and still see claims deserted since I moved in with saw racks and whittling benches which have lasted for weeks.
I don't see any indicator to repair stuff.. have I been vandalised or does this stuff just disappear?
So far, one of my drying racks disappeared. No biggie, but when it disappeared I had heaps of stuff lying around so it didn't strike me as likely that someone took it.
More distressing: tonight my ore smelter is gone.

And yet, I often see and still see claims deserted since I moved in with saw racks and whittling benches which have lasted for weeks.
I don't see any indicator to repair stuff.. have I been vandalised or does this stuff just disappear?