Wow... Thank you very much!
My Tiled version was 0.14.2, but the columns attribute was only added in 0.15.
Regarding the transparency, I met another interesting phenomenon.
Only when I add this:
// optional drawing
after the mapRenderer Draw call, will the tiles be transparent. Black background is gone. I don't know why, but it works now.
I just realized if I do it like this:
mapRenderer.Draw(map, ref viewMatrix, ref projectionMatrix);
It works too, plus I can set the parameters of Begin, e.g.
To render the zoomed map without blur.