Mine was bent and straightened several times until the top weld finally let go. I then got a total replacement.
I was told that the cause of this (in my case) was dropping down into a sharp dip. As you go over the lip, the mower lifts up and the tail wheel swings around backwards. As you head down through the dip, the tail of the mower then slams down on the ground with the wheel still facing the wrong way, which makes the wheel assembly pivot around, quite forcefully, sometimes bending the forks in the process. I now make sure that there is lots of slack in the toplink chain on the mower, to try to keep the wheel on the ground all the time, and also make an effort to ease through dips a bit more gently...so far, so good.
The alternative way to bend the forks is to back into something just right (or wrong!).
BOB