transform.localRotation = Quaternion.RotateTowards() or Quaternion.Euler fails on vertical axis

I would like to make straight rotations @ 0, 90,180 and 270 on each axis at the click of a button. I have created 4 buttons (up, down, right and left) and when I click each, my object rotates 90 degress to the direction chosen and then stops.

My issue is that when the object is vertical (standing up) and I click on right or left, instead of "falling" to the right/left, it rotates on its axis (it spins); however, that doesn't happen if the object is on the "floor".

Attached is the code for the buttons and the code for the Player Control.

Please help!` This is the position that gives me problems When is lying down, it is fine

 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;
 using System.Collections;
 
 public class Button : MonoBehaviour, IPointerDownHandler {
     public bool clicked;
     public virtual void OnPointerDown(PointerEventData ped) { clicked = true; }
 }

 using UnityEngine;
 using System.Collections;
 
 public class PlayerControl : MonoBehaviour {
 
     private float rotSpd = 200f;
     public Button btnUp, btnDown, btnRight, btnLeft;
     private float rotX = 0f;
     private float rotY = 0f;
     private Quaternion qTo = Quaternion.identity;
 
     void Update () {
         if (btnDown.clicked)     { btnDown.clicked     = false; rotY += 90f;}
         if (btnUp.clicked)         { btnUp.clicked     = false; rotY -= 90f;}
         if (btnRight.clicked)     { btnRight.clicked     = false; rotX += 90f;}
         if (btnLeft.clicked)     { btnLeft.clicked     = false; rotX -= 90f;}
         qTo = Quaternion.Euler (rotY, rotX, 0.0f);
         transform.localRotation = Quaternion.RotateTowards (transform.rotation, qTo, rotSpd * Time.deltaTime);
     }
 }