tsvector string representation and parsing

Hi,

I am constructing a tsvector representation of some text manually 
because I need to provide explicit positional parameters. In some cases, 
the conversion fails and I get a "syntax error in tsvector".

This is a minimal example that goes wrong (but shouldn't IMHO:

> SELECT format('%L:1', '\:')::tsvector

My expectation here is that %L would transform '\:' into a correctly 
formatted character string, including single quotes around the string. 
The documentation reads:

> L quotes the argument value as an SQL literal

> SELECT $$'\:':1$$

returns «'\:':1», but

> SELECT $$'\:':1$$::tsvector

returns «':':1», so something is happening here inside the single-quoted 
lexemes to the backslash. My understanding is that everything inside 
single quotes is taken as a lexeme. From the documentation:

> To represent lexemes containing whitespace or punctuation, surround them with quotes

So having everything surrounded by single quotes (followed by a 
positional argument after the colon), «$$'\:':1$$::tsvector» should 
actually return a vector with a single lexeme «\:» at position 1.

Am I missing something?

Regards
   Johannes