Facebook location change bug
It seems that Facebook runs into memcached issues when you update your location to a new city. I recently moved to Boston and for the sake of maintaining correctness on my Facebook profile, I decided to change the city I'm living in. Soon as I started getting likes on a newsfeed as trivial as this, I decided to simply delete the post (and of course not 'Hide from Timeline'.) What happened next was that the likes kept pouring in, I kept getting the notifications, but clicking on the notifications led me to the Facebook 404 page. I asked my room mate to check if he can see this from his newsfeed and yes, it was there for him to see and like (and comment on!) Even about 8 hours later, the post that I moved to Boston lives on my friends' newsfeeds.
Next, we replicated this bug by my roommate changing the city he lived in and then deleting the post - and yes, it was still there on mine and his other friends' newsfeeds.
Clearly, this is a bug from a UX point of view. Looking at bugs in successfully scaled systems and trying to back-work an explanation for the same is a good idea for enhancing your understanding in scaling up systems and writing appropriate tests so that we entrepreneurs don't make such bugs while scaling up - which a lot of smart engineers at Facebook were unable to detect and rectify. What do you guys think is Facebook doing wrong here? I don't think this applies to other items such as Photos, status updates etc.