PHP: Namespaced classes, class loading and exceptions causes weird behaviour

I witnessed some strange behaviour regarding PHP's exception handling in a recent project. Case goes as follows.

In my app, I use namespaces. All classes are in individual source code files. The code relevant to this particular case, is spread over 3 classes.

The "outermost" class is a dispatcher (or router), which wraps the dispatch call inside a try-catch block. The dispatched request, calls a method in a third class, which runs code (wrapped in a try-catch block), which causes an exception.

Because I had omitted a use Exception; statement in the class where the error happens, the thrown exception trickles all the way back to the outermost layer (the dispatcher), where it is caught - causing me to scratch my head why the catch around the code causing the error isn't working.

To me this seems strange. Logically, PHP should in this situation (IMO) throw a Class not found exception/error, leading me to the actual error in my code, instead of trying to "stay alive" as long as possible.

Should this be filed as a bug, or is this expected behaviour?

Edit: Code example

File: class-a.php

<?php 
namespace hello\world;

class classA {
    protected $b;

    public function __construct() {
        $this->b = new \hello\world\classB();
    }

    public function doSomething() {
        try {
            $this->b->throwException();
        } catch (Exception $e) {

        }
    }
}

File: class-b.php

<?php 
namespace hello\world;

class classB
{
    public function throwException() {
        throw new \Exception("bar closed");
    }
}

File: run.php

<?php 
include 'class-a.php';
include 'class-b.php';

$a = new \hello\world\classA();

$a->doSomething();

ClassB throws an \Exception in ClassB::doSomething(), for which ClassA has a catch-clause, but because ClassA doesn't declare use Exception or catch (\Exception), the catch doesn't match and execution ends with a Uncaught exception error¹. But in my opinion, it should cause a Class not found error.

I might be expecting too much of the permissive PHP compiler, but it would help in tracking down silly errors that should be easy for the compiler to spot.

¹ If the $a->doSomething() in run.php was surrounded by a try..catch clause, the Exception would (or at least could) be caught there, since it trickles down the stack.