Missing UV-information after export to G3DJ

Hi there,
I exported a simple model from blender to FBX. The model contains a UV-mapping. I reimported the FBX file into a clean blender project to check if the UV config is exported correctly - and it is:

The screenshot shows, that the uv information is correctly exported in the FBX file and Blender renders the model correctly.

However, if I use FBX-Conv to convert to G3DJ with
../fbx-conv -f -v -o G3dj ./uvmap.fbx ./uvmap.g3dj
the uvMapping attribute is empty:

	"materials": [
		{"id": "Material", 
			"ambient": [ 0.050876,  0.050876,  0.050876], 
			"diffuse": [ 0.800371,  0.029121,  0.000000], 
			"emissive": [ 0.000000,  0.000000,  0.000000], 
			"opacity":  1.000000, 
			"specular": [ 0.800371,  0.029121,  0.000000], 
			"shininess":  25.000000, 
			"textures": [
				{"id": "base_color_texture", 
					"filename": "UVImage.png", 
					"type": "DIFFUSE"}
			]}
	], 
	"nodes": [
		{"id": "Cube", 
			"rotation": [-0.707107,  0.000000,  0.000000,  0.707107], 
			"parts": [
				{"meshpartid": "Cube_part1", 
					"materialid": "Material", 
					"uvMapping": [[]]}
			]}
	], 

Is this a know limitation, a bug or am I missing something?

Thank you!

Btw, the output of fbx-conv is the following:

INFO:     FBX to G3Dx converter, version 0.01.0000 x64 , FBXSDK 2019.00
STATUS:   Loading source file
STATUS:   FBX file version 7 4 0
PROGRESS: Import FBX 100.00%                                                             
STATUS:   [Cube] Triangulating FbxMesh geometry
VERBOSE:  [Cube] polygons: 12 (36 indices), control points: 8
STATUS:   Converting source file
STATUS:   Closing source file
VERBOSE:  Listing model information:
VERBOSE:  ID        : 
VERBOSE:  Version   : Hi=0, Lo=1
VERBOSE:  Meshes    : 1 (24 vertices, 1 parts, 36 indices)
VERBOSE:  Nodes     : 1 root, 1 total, 1 parts
VERBOSE:  Materials : 1 (1 textures)
STATUS:   Exporting to G3DJ file: ./uvmap.g3dj
STATUS:   Closing exported file

Start with the reported fbx-conv command and the FBX-to-G3DJ conversion path, reproducing the provided UV-mapped Blender/FBX example. Inspect how the converter transfers UV data into the G3DJ mesh part and verify the result against the shown empty uvMapping output. Done means the converted G3DJ contains the source UV information.