Why does this C++ snippet compile (non-void function does not return a value)

Question

I found this in one of my libraries this morning:

static tvec4 Min(const tvec4& a, const tvec4& b, tvec4& out)
{
    tvec3::Min(a,b,out);
    out.w = min(a.w,b.w);
}

I'd expect a compiler error because this method doesn't return anything, and the return type is not void.

The only two things that come to mind are

In the only place where this method is called, the return value isn't being used or stored. (This method was supposed to be void - the tvec4 return type is a copy-and-paste error)
a default constructed tvec4 is being created, which seems a bit unlike, oh, everything else in C++.

I haven't found the part of the C++ spec that addresses this. References (ha) are appreciated.

Update

In some circumstances, this generates an error in VS2012. I haven't narrowed down specifics, but it's interesting, nonetheless.