I use the Highwayman’s Hitch as my quick release knot, but ALWAYS stick the rope tail THRU the loop to prevent what you describe. I never let the rope tail just hang from the quick release knot. Too easy for bored horse to release the rope.
I do use up rope tail doing more “crochet loops” on that first loop by the knot, still put the rope tail thru the last loop. I have rather long tie ropes, don’t want the tails dragging on the ground when tied. Doing more loops, even if horse pulls the tail end, it just tightens THAT LAST loop, not the whole chain of loops to the knot.
I have been really happy with the Highwayman’s Hitch knot, since changing over from my old 4-H quick release knot that got bound up when horse pulled hard. I was never really happy with that side effect in case horse needed to be loosened quickly. I found the Highwayman’s Hitch when searching for alternative knots myself to teach the present generation of 4-H kids.
I have not had the Highwayman’s Hitch bind up using synthetic or cotton ropes, even with some horses really sitting back on them. My Trail Rider friends have also been really happy with the knot, no binding up there either when you have to get a horse loose fast.
But without tucking the tail thru that last loop, tightening it a little, horse WILL be able to get loose pretty easily with any quick release knots. That is what they are made to do! She may figure out how to get the tail out of loop, with time. But you get a bit of slack time, as she works her way up the ladder of loops to the knot for a final untying!!