Hi Werner,
This is not specific to the '\' character - any non-whitespace character will have the same effect (e.g. "this text*is not bold* "); as specified in section 6.2:
"…
The opening styling directive MUST be located at the beginning of the parent block, after a whitespace character, or after a different opening styling directive. …"
So there is no styling because the '*' is not immediately after a whitespace character.
However, the inclusion of a formal grammar would make implementing a parser easier and help to clarify cases like this.
(The reason for escaping with '\' comes from the C language, where it was useful to be able to represent ASCII control characters using printable characters, specifically "\n" to produce a line-feed, plus others; but then comes the need to represent a literal
'\' character that is not an escape, and thus "\\" escapes a literal '\'. Escaping characters in the context of human-to-human communication seems less appropriate.)