How can constructor definitions from traits collide?

How can constructor definitions from traits collide?

In PHP 5.4.9, the following example triggers the fatal error "B has
colliding constructor definitions coming from traits".
trait T {
public function __construct () {
echo __CLASS__ . ": constructor called.\n";
}
}
class A {
use T;
}
class B extends A {
use T;
}
There's no problem when the trait contains a different method than the
constructor, and no problem when the constructor is actually copied into
the classes (without using traits, the "language-assisted copy & paste"
feature).
What's so special about the constructor here? Shouldn't PHP be able to
figure out that one of them overrides the other? I couldn't find anything
about this limitation in the manual.
This related question mentions a way to get around the problem (by using
aliases for trait methods), but not what's causing it in the first place.