There is some kind of check that happens when an account is deleted, which results in the "User is globally banned" message. For some reason, it is not just checking for a sitewide ban, it checks for any ban.
If your account has been banned in one subverse, you will get the globally banned bug when you try to delete your account. I am not really sure what process is going on when accounts are deleted, but I don't see why this wouldn't be a simple fix.
Also if you want to test this, create two new accounts. Ban one of the accounts in a subverse you moderate, and then try to delete both. Your banned account will get the global ban message.
Edit: I suspect that this may be caused by a change to how sub bans are handled rather than the account deletion being handled in a different way. I know some people were able to delete accounts that had been banned, so perhaps this only has an effect on accounts that were banned in a sub after a certain date (when whatever is causing the issue was created/changed).
Edit 2: I have now tested this a few times and it can be consistently reproduced. One other thing I tried is using the delete page to try and delete an account whilst logged into a different account. It gives you a field to enter a username and a password, so I thought using it from another account may get you around the global ban bug, but instead it will give you "User not found", or something to that effect. I will carry on testing to see if there is a temporary workaround.