printing array of strings with writefln?

[Ivan Kazmenko via Digitalmars-d-learn]

On Sunday, 16 November 2014 at 15:08:10 UTC, JR wrote:
> On Sunday, 16 November 2014 at 14:16:55 UTC, Artem Tarasov 
> wrote:
>> writefln("%(%s-%)", ["a", "b", "c"]) doesn't print the 
>> intended a-b-c but surrounds each string with double quotes - 
>> "a"-"b"-"c", which I find inconsistent with the fact that 
>> writefln("%s", "a string") prints the string without any 
>> quotes.
>> How do I get the desired behaviour using just the format 
>> string?
>
> writefln("%-(%s-%)", ["a", "b", "c"])
>
> http://ddili.org/ders/d.en/formatted_output.html

What I find surprising is that "%-(ch%)" without %s inside also 
works, although ch is prepended to each string and not a 
separator (which makes sense, but still).  This does not seem to 
be mentioned in the documentation, neither in Ali's book.  Is 
this a bug?