Why does ImportString produce Notebook[{}, StyleDefinitions -> "Default.nb"

While chasing down another question , I attempted to trick Mathematica into accepting its own TeXForm with the attached notebook. However, it produces an output that I don’t comprehend.

Notebook[{}, StyleDefinitions -> "Default.nb"

What does this mean? Did it successfully import its own TeX string? If so, where can I find it and how can I use it in my current notebook?

&Wolfram Notebook

It is a bug. Please report this to the support.