Laravel resolve helper returns string

I have a binding in my AppServiceProvider:

$this->app->bind(
    'App\Services\Avatars\Contracts\AvatarServiceInterface',
    'App\Services\Avatars\GravatarAvatarService'
);

If I inject the AvatarServiceInterface into a controller constructor or method then it correctly returns an instance of the GravatarAvatarService class. However, if I try to use the resolve helper in a controller method (or anywhere else for that matter), e.g.:

$instance = resolve('App\Services\Avatars\Contracts\AvatarServiceInterface');
var_dump($instance);

...it is just returning a string of whatever I'm asking it to resolve. In the example above it returns:

'App\Services\Avatars\Contracts\AvatarServiceInterface' (length=53)

The resolve helper was working for me up until a few days ago. I've tried running composer update to get the latest version of the framework but that hasn't solved this issue.

Anyone have any ideas?

via Chebli Mohamed