I have a User and a Trip model with belongsToMany relationships and a pivot table between. I'm trying to get Trips that have been modified since the User joined (ie since the trip_user record was created). In the Trip model I have the following scope:

public function scopeModified($query) {
    return $query->where('trip_user.created_at', '<', 'trips.updated_at');
}

This is how it's called ($user is the current user):

return $user->trips()->modified()->get();

This always returns all of the User's Trips.

What's strange is that when I log the query with DB::getQueryLog(), it spits out the exact right query:

select `trips`.*, `trip_user`.`user_id` as `pivot_user_id`, `trip_user`.`trip_id` as `pivot_trip_id`, `trip_user`.`created_at` as `pivot_created_at`, `trip_user`.`updated_at` as `pivot_updated_at` 
from `trips` 
	inner join `trip_user` on `trips`.`id` = `trip_user`.`trip_id` 
where `trip_user`.`user_id` = ?
and `trip_user`.`created_at` < ?

with the bindings ["3","trips.updated_at"]

if I copy this query and run it directly in MySQL, I get the results I want. But running return $user->trips()->modified()->get(); always returns all the trips.

Any thoughts would be appreciated. I know this is a tough one to describe or replicate without the rest of the code.