What is it with German carmakers and four-door cabriolets? Our discovery of patent drawings for a topless Porsche Panamera is the latest in a series of wild proposals that started with the very limited run Maybach Landaulet.

In 2007 Mercedes revealed the Ocean Drive, a true four-seater convertible with a folding fabric roof. The global crunch probably but paid to that S-class based idea, but there are also rumors around that Audi would like to do something similar on its upcoming A7 big four-door fastback.

Aside from a signs of a weird fascination with classic four-seat, four-door convertibles such as the 1960s Lincoln Continental, the German carmakers seemed to be doing nothing more useful than making life very difficult for their engineers.

Trying to make a respectably stiff car out of a structure with no roof pillars and two door apertures on each side must be close to impossible. A secondary bulkhead directly behind the front seats has to be a possibility.

And then imagine designing a roof long enough to stretch from boot to windscreen that’s also neat enough to be bundled up without robbing all the boot space.