Rig shows gaps between meshes when animating after export

[mysticfall]

OS:

Manjaro Linux

Godot version:

master / https://github.com/godotengine/godot/commit/d711c57d767734887fbf0955a7b9902c54498a0d

Blender version:

2.81

Issue description: I have a humanoid model whose mesh is separated at the neck line. I added a data transfer modifier to match normals between the meshes and it looks and animates ok in Blender.

However, when I export it to Godot in .escn, it shows a gap between the meshes. It seems to look fine at first, but as soon as I play any animation, the head part gets separated from the body, leaving a visible gap.

A similar set up didn't show such a problem when exported using Blender 2.7x with the older version of .escn exporter, by the way.