The "frame" object of the experimental "minecraft:icon" component in items within the behavior pack resorts to using the first frame of the specified texture. For example, if the "sword" texture is set as the value of "texture," the icon will display as a wooden sword regardless of the "frame" value.

{
  "minecraft:icon": {
    "texture": "sword",
    "frame": 1
  }
}

The above should set the item's icon to the stone sword's; however, the item's icon is instead set to the wooden sword's.