Correct me if I am wrong, but my notifications are flooded from all sites I am in within the stackexchange network, have a look at the screenshot.
It is not a bug. You have reached 200 reputation on one account for the first time (at GLU, in this case) and receive an association bonus of 100 for all of your accounts (including GLU). If you create a new account on another site, your reputation will start at 101 instead of 1.
All your sites giving you a notification may be a bit much, but most people don’t have that many accounts by the time they reach 200 on one of them. Also, it won’t happen again in the future.