When you knock a Invasive Hardhead or Feral Hardhead down to a low enough HP that it becomes a rideable mount it seems more difficult than necessary to dismount it. There is no vehicle exit button, pet control button, or other obvious means of dismounting. Plus you don’t dismount it by trying to get on a normal mount or using Travel Form on a druid. You are stuck until you click off the Covered in Dirt buff (which doesn’t mention it’s related to your current mount) .
I suspect some players are frustrated by the current behavior because they can’t figure out how to get off the creature.