Several weeks later (this morning) I went to move it, in order to make room for my china white elephant, when I noticed drifts of fine, black 'powder' all over and around the knob. Lots of black powder in fact, looking like carbon. I'm guessing the fungi has spored. I was instructed to 'get that thing out of the house!' and so the photo doesn't show the sporing thing in situ but held between my thumb and forefinger, outside.
Can anyone throw some light on this phenomenon?
Here are the two significant images.