The explanation was annoyingly simple. I'd been setting up a new blog for my pal Jurij (he's not said if he likes it yet, so it may simply be strangled at birth) and had foolishly taken no steps to dissociate my own identity from it. Blogger didn't do this to me before - I already run two blogs, and to my knowledge I never appear as frankenstina - but the new Blogger is disturbingly more akin to Wordpress in its complexity (and no doubt in its flexibility) and strange things are happening. F'rinstance, the box I'm currently posting in doesn't look the way it always has - to the extent that I'm wondering if this post is going to arrive on the wrong blog.
If it doesn't, and if I've reverted to my former persona, then all is well. But note to self: don't set up new blogs in the middle of a telephone conference. And don't work on them after midnight.