This bug is reported on Japenese Wikipedia.

When you search a page with lower case name, you can got the upper case one. (e.g. Both of "Special:Search/WP:CNJS" and "Special:Search/wp:cnjs" show "Wikipedia:Help for Non-Japanese Speakers").
This is fine.

But in case of "WP:Lua" (redirecting to "Wikipedia:Lua"), I cannot get it by lower case version "Special:Search/wp:la". Below is ther OK/NG list;

• "WP:Lua": OK (This is the actual name)
• "WP:lua": OK
• "WP:LUA": NG
• "Wp:Lua": NG
• "Wp:lua": NG
• "Wp:LUA": NG
• "wp:Lua": NG
• "wp:lua": NG
• "wp:LUA": NG

What is the difference? Isn't this a bug?
or how can I resolve it?

thanks