Arch adding 2 walls: results in incorrect shape

[JLB85FR]

hello,
Adding 2 walls with the '+' button in Arch, results in an incorrect shape displayed (one of the walls in made of an extrusion with a Bezier curve). if selecting the 'cut', the 2 shapes (result and cut) do not correspond (see pictures below)

The actions to perform are:
- select Arch workbench
- select 'cut_porche_est'
- select+ctrl 'wall001_house'
- Add (+)

it's similar if adding 'cut_wall_arche_nord' to wall001_house

and 2 other questions:
- why do the 'cut_porche_est' and 'cut_wall_arche_nord) colors stay gray, while the color property of the shapes is yellow (255,255,127) ?
- I cannot add the 2 cuts (cut_wall_arche_nord + cut_porche_est), '+' button has no effect, is this normal ?

OS: Windows XP
Word size of OS: 32-bit
Word size of FreeCAD: 32-bit
Version: 0.16.6651 (Git)
Build type: Release
Branch: master
Hash: a69ee20f0c2acf146c935633ff43f933a8b14316
Python version: 2.7.8
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17