Trundle Ult Toggles On and Off While In Use [GAMEPLAY]

I just started playing trundle support recently but I have noticed that in the past few days when I ult and move Trundles ult toggles on and off. I want to play him in ranked but now Im afraid to since his ult is now unreliable. Please check into it. In the video you can see the items I bought and how I moved and the target i picked. I have more videos of this glitch. If you need more info or videos I would be glad to provide you with it.