[NTG-context] 3SIDE imposition schema weirdness

[Nicolas Girard]

Hi,
i'm a little bit puzzled by the results of the following test file,
using the 3SIDE imposition schema from Willi (
http://wiki.contextgarden.net/Imposition#Additional_schemas ).
The results consists in pages 1|2|3 on the recto of the sheet, and
pages 4|5|6 on the verso.

* Is it really the intended result ?
* If so, I don't understand how can \dosetuparrangement{3}{1}{6}{4}{2}
give 1|2|3 // 4|5|6 . What's the rationale ? Why no page 5 among the
arguments of \dosetuparrangement ?
* What if one wants to fold the resulting brochure ? How to adapt the
code (besides by try and error) for the resulting arrangement to be
3|6|1 // 2|4|5 ?

Thanks in advance,
cheers,
Nicolas