Question about sen fortress boulders

i made my way to the part in sens fortress where i can push a lever to change the direction of the boulders

I did that and thought that the previous path would now be safe to walk on

But when i walked down that path i got hit by a boulder and when i made my way back up the lever had reset to its original position

Now i am wondering if this is a bug or not

Because it would be disappointing otherwise