When a mod is given the dialog to merge an account with another, they typically prompt for the "master" user.
Most of the time, we simply copy/paste the URL of the user into the box and all is well.
The dialog currently allows one to enter the URL for another site in the Stack Exchange network and then attempt to try and merge them.
However, the logic parses the user id out of the URL and nothing else, merging the account with another user on the same site.
This results in an improper merge, which as we can all agree, is not a good thing.
Please fix this so that when merging accounts, you use only the user id, or, if there is a URL, that the domain of the URL matches the Stack Exchange site exactly.