Precipitate in my KRST stock

This morning I noticed some fine dark precipitate in an unopened bottle of KRST stock I purchased one year ago. It's stored in a very temperature-stable location in my basement that stays between 62F to 70F over the year. A partially used bottle from 2008 is precipitate-free. The newer bottle is the squarish style and feels thinner, while the older one is the stout round bottle; both are HDPE. Is the stock solution oxygen sensitive? I can imagine the wimpier new-style bottle is more air permeable.

a quick search reveals this thread:
(there was a url link here which no longer exists)

Yes, I should remembered that recent thread. My question is slightly different - why has a 6-year-old bottle not thrown precipitate while a 1-year-old bottle stored in the same environment started doing so? The newer bottle is thinner - is the slow diffusion of oxygen through the bottle playing a role?

The cause is a combination of things. Pinpointing the exact one would be difficult or impossible. However, due to the difference in age the two bottles must be from different batches. Their individual histories would be different before you purchased them.

My KRST, both stock and diluted, are in glass. I have no problem with precipitation.