why the wall almost got no support at all ??

[psychotik2k3]

Hi, i have a simple model which is a horizontal plate and it got some tiny walls 1.5mm thick 20-30cm long vertically on top of that.

tha problem is that simplfy slice this as this way top layer of the plate got holes where the walls will be, and so when the wall starts to be built, only it's external wall is overlapping the bottom layer, and the inside layers (my wall is made of 4 layers)
i ma de a youtube video to show that.
https://youtu.be/SiKxBbYThp4
is there a way to prevent this ? because in my example the layer is making a 90° turn whith no other support than the external layer.