If I go to MathOverflow from another SE site by clicking on the link in “Your Communities” under the right-most menu on the top-bar, I do not end up with the usual
https://mathoverflow.net, but with a strange URL such as
The string is different each time. The same happens when I go from MathOverflow to MathOverflow Meta or vice versa, but not when I go to any other SE site.
What is the meaning of this? Is it a bug?
EDIT: It’s not just MathOverflow. It also happens when I go from other sites to Server Fault or Ask Ubuntu, so it appears to affect all Stack Exchange sites with their own domain. Since it is not MO-specific, I reposted the report on Meta SE.