Its interesting to note that this seems to happen more frequently or perhaps is more noticable with paperweights than other forms. Interesting also that it's not just Chinese glass it happens with.
In previous discussions it was noticed that yellow colours are often involved when this occurs. I am interested in yellow glass of all shades and have one thick walled item which is oily and rather cloudy. How might yellow colour(s) tie in with the chemicals mentioned above ?
In yet another discussion, I seem to remember that the development of a very pale yellow colour in pressed glass over time could be associated with an excess of arsenic, ironically, originally used as a clearing agent.
PS Incidentally, I can attest that Leni's home enjoys the benefits of central heating and double glazing which ensures that its warm and not at all damp, despite the English winter.