So, Badmother, the defining characteristic of the mixte is a three stay rear triangle setup ? Not sure everybody will agree with that. You might be right of course, but my understanding of mixte is the angle/height of the straight TT as opposed to the curved swan neck stepthrough, or similar. In a pile rusting away somewhere, I have several three stay stepthroughs dating 1930's.

Regarding the "normality" issue, and this is pertinent to the mixte vs stepthough "debate", the norm is what the vast majority do and is therefore considered to be normal, whether this majority behavior is of choice, or peer-pressure induced. The norm until quite recently, and most definitely in the early days of cycling, was for women to wear (longish) skirts, which rather hindered swinging a limb over a straight TT. I think that you will find that the "mixte" boom occurs at the time when women started wearing pants (trousers). That would make the mixte most politically correct, a kind of material reminder of the ultimately successful fight for rights of the suffragettes. And with that, I rest my case.