There is no explanation about what can be entered in the Search field at the bottom left of the Manage Users page.
The label "Search" let me think that I could enter only part of the name or use jokers like "*" or "%".
Only after looking at the code, I understood that I have to enter either the exact Id (which means that this is pointless for a search function), the user name or the user email.
either change the label "search" or update the documentation.