This has been going on for far too long.
When you try to modify a block on a user who is already blocked, while the text "This user is already blocked! Do you want to change the settings?" will appear, it will not change the settings, but will instead place a new block, the log entry reading "X blocked Y" instead of "X changed block settings for Y". This results in two entries on Special:BlockList, both blocks affecting the user, and if the user later needs to be unblocked having to do so twice.
The current system of having to unblock (sometimes multiple times) then block again is janky. I am not sure what is causing the issue, but it only happens on testwiki.wiki and must be something local