Complicated to explain, therefore:
Steps to reproduce (proSilver):
I.:[list: 7bcf6]

• MCP
• User notes
• select a user
• click on "User details" in menu
• => "The requested user does not exist."

Slightly different steps, same result and another interesting thing:
II.:[list: 7bcf6]

• MCP
• User notes
• select a user
• enter & submit note
• click "Return to the previous page" 1)
• click on "User notes" tab
• => there still is a "User details" link in menu
• click on this link
• => "The requested user does not exist."

subSilver2:
I: doesn't work since the menu entry is no link
II: follow the steps up to 1), then:
[list: 7bcf6]

• click on "Reported posts" (or other menu entries like "Moderation Queue" and so on)
• click on "User notes" menu entry
• => there still is a "User details" link in menu
• click on this link
• => "The requested user does not exist."

Nice, isn't it? :razz: