That is a bug. Thanks for reporting it. To fix it on yours -
in tk2dTextMeshEditor.cs, look for this line:
textMesh.renderer.material = allBmFontImporters[newId].material;
and replace with:
textMesh.renderer.material = allBmFontImporters[newId].data.material;
That should fix it.
p.s. I edited your post above to remove the project. If you want to post full projects, either use email or the private support forum. Thanks.