Landscape Weight Maps are turned to 8bit when exported from UE4

I’m using version 4.15.2 of UE4.
I made a Landscape using a basic height map and additional flow maps that are all
greyscale 16 bit png formats. Those additional maps are used to define areas where
a specific texture is needed. I use a Landscape layer blend for the material applied to
the landscape as shown in many tutorials and everything is fine, but…
After the landscape is imported in UE4, a problem happen when I try to re-import those
additional maps through Landscape editor paint tool. The landscape looks completely changed.
I noticed that if I export the flow map from UE4 before I reload it, no particular problem seems to happen
except that UE4 convert the initial 16 bit file to a 8 bit file. I wonder if it is normal.
The flow map is done with World Machine (png greyscale 16 bit) and used without any tweaking in Photoshop.
There’s not such a problem if I try to reload the height map in the sculpt section of the Landscape editor.
A I doing something wrong? I would like to be abble to use a 16 bit greyscale for the layers if possible,
without having UE4 converting them to 8 bit.