Mine tend to hide after molting, so while I've never seen this, it is possible i've merely missed it. Is it a sling? if everything else is in full working order, it is probably ok. good luck. my P. fasciata sling ate one of her legs a couple of days before molting, and now it won't let me check its progress.
The reason I ask is because a couple years ago, I received
a beautiful B. smithi 4 inch critter who must have somehow
injured himself in transit. When I went to get him out of the container, he decided he only needed 7 legs and the 8th leg remained in the container. I quickly named him Siete (spanish for Seven).
When he molted, he grew the 8th leg, but it looked nothing like
the other seven legs. In fact, it looked more like a thin black stick.
A couple molts after that, it looks like a normal leg again, though
if I look closely, I can see it doesn't have quite a much color on it as the other 7 legs. I think after the next molt, it will be impossible to tell he ever lost it to begin with.
P.S. If you want to see the "black stick" you can check out my