where between in query builder using date values is not working as expected.

I'm trying to get the data between 2 dates.

and this code returns 0 results

return Model::whereBetween('created_at', [$this->carbon->startOfWeek(), $this->carbon->endOfWeek()])->get();

this is the query statement it creates when I use toSql();

select * table where created_at between ? and ?

but this query works

return $this->appointment->whereRaw('`created_at` between "' . $this->carbon->startOfWeek() . '" and "' . $this->carbon->endOfWeek() . '"')->get();

this is the query statement it creates when I use toSql();

select * table where created_at between "2017-07-31 00:00:00" and "2017-08-06 23:59:59"

I don't get why the first one doesn't work but doing whereRaw works but they have the same query statement.

Its exactly the same and its bothering me.

is this a bug?