Scala priority queue with in the order dequeue

Scala library has priority queue implementation, but when priority are equal the dequeued items are not in the same order with enqueue order:

import scala.collection.mutable

class PriorityQueueTest{
 implicit val ord: Ordering[(Any,Int)] = Ordering.by(_._2)

 var queue = mutable.PriorityQueue[(Any,Int)]()

}

val pQueue = (new PriorityQueueTest())
val queue = pQueue.queue

queue.enqueue(("a",3))
queue.enqueue(("b",3))
queue.enqueue(("c",3))
queue.enqueue(("d",3))
queue.enqueue(("e",3))
println(queue)
//PriorityQueue((a,3), (b,3), (c,3), (d,3), (e,3))
queue.dequeue()
//res6: (Any, Int) = (a,3)
println(queue)
//PriorityQueue((e,3), (b,3), (c,3), (d,3))
queue.dequeue()
//res8: (Any, Int) = (e,3)
println(queue)
//PriorityQueue((d,3), (b,3), (c,3))

How to get the dequeue with same order:

import scala.collection.mutable

class PriorityQueueTest{
 implicit val ord: Ordering[(Any,Int)] = Ordering.by(_._2)

 var queue = mutable.PriorityQueue[(Any,Int)]()

 def inplaceDeque(number:Int): Seq[(Any,Int)] ={
  var res: Seq[(Any,Int)] = Seq()
    res =queue.take(number).toSeq
    queue =queue.drop(number)
  res
 }
}

val pQueue = (new PriorityQueueTest())
val queue = pQueue.queue

queue.enqueue(("a",3))
queue.enqueue(("b",3))
queue.enqueue(("c",3))
queue.enqueue(("d",3))
queue.enqueue(("e",3))
println(pQueue.queue)
// PriorityQueue((a,3), (b,3), (c,3), (d,3), (e,3))
pQueue.inplaceDeque(1)
// Seq((a,3))
println(pQueue.queue)
// PriorityQueue((b,3), (c,3), (d,3), (e,3))

Question

Why Scala library doesn’t implement in order dequeue for priority queue?
How to implement the Scala priority queue library?