tuple (TypeTuple kind) multi-initialization. Actually documented?

[monarch_dodra]

If you declare an instance of a tuple, eg TypeTuple!(int, int, 
int), you can initialize all members from a single argument. EG:

TypeTuple!(int, int, int) a = 5;

bearophile made a suggestion that we should deprecate this.
https://d.puremagic.com/issues/show_bug.cgi?id=6367

I'd like to know if this behavior even documented at all, or kind 
of "just happens to work".

In particular, it doesn't work in CTFE at all:
https://d.puremagic.com/issues/show_bug.cgi?id=12499

I'd like to ask the spec guru's to know which direction to take 
in dealing with both these issues.