I guess I worded that incorrectly- I wouldn't consider it normal because he's a walker for falling to his knees, but the smaller trips could just be from being off balance.
If he's constantly tripping (like every time he's ridden, multiple times he's ridden) then no, I wouldn't write it off to being a walker. I just wanted to pop in and say that walkers can trip more often (from my experience) when not balanced by their rider.
I don't believe the walkers there are left with long toes, as I remember one of the BO's asking the farrier to not leave long toes, if he does, we have him correct it.
Please don't take just my advice into consideration, I probably should have stayed silent, but I did want to offer what I know about walkers into the conversation. I am by no means an expert, but after riding alongside them for many years, I have picked up knowledge here & there.
Best of luck, OP, sorry for any misunderstanding. Hope this problem gets sorted out and you have many good rides with your TWH.