Invisible words when using Markdown explanation in a node

[Necior]

Steps to reproduce

1. Open https://play.d2lang.com;
2. Paste the following snippet in the editor:

example: {
  explanation: |md
    *one* __two__ three!
  |
}

3. Compile the diagram.

Observed behavior

The following image gets rendered:

Please note that the word "three" is not visible in the picture.

Expected behavior

The word "three" is visible in the picture.

Additional comments

I've observed the same behavior in every available engine (Dagre, ELK, TALA). I've tried using D2 locally (with version 0.4.2). The result is the same.

What is more, please note that changing "three" to a longer string (e.g. "threeeeeeee") will make the resulting node wider while the word is still invisible:

[bo-ku-ra]

this is a strange specification for the D2 and has not been improved. (#1431)
i add "<br/>" to get around this.
i do not know why.

https://play.d2lang.com/?script=Sq1IzC3ISbVSqOZSUEitKMhJzEsEhaGVQk1uCpeCgoKCVn5eqpZCfHxJeX58vEJJRlFqqiJYwiapSN-OS0GhhquWCxAAAP__&

[alixander]

@Necior appreciate the 💯 bug report!