|I'm not too fussed about Best Answer, just mentioned in passing that it marks the thread as solved.|
However, I think it very likely that the "Fixit" in #5 initiated the cure to the problem. As given in #9, the icon cache does not always immediately build into its new larger space allowance, so the "symptom" remains - it often takes a few boots before it rebuilds and uses it, so the problem looks as if it suddenly cured itself. This is probably what happened, so there was no longer any need to "force it" to rebuild using the link in #7.
I am fairly convinced that you will not run into it again now you have a larger cache - but only time will tell.
Always pop back and let us know the outcome - thanks