This has been buggine me for a while already: the MP search box behaves very differently from the in-game Beatmap Search.
At the moment, the MP search seems to only respond to Room Title, Artist, Song Title and Difficulty, not the Tags. Say if I want to look for a Touhou room and I type "Touhou" into the MP Search this is what I get:
But when I change the keyword to "Lunatic":
As you can see from the example, the MP search function did not recognise Touhou tags (unlike the main search box in the client). The MP search function will be a lot more useful with the Tags capability imo.
EDIT: Changed Title texts for better description + minor edits. Original Title: "Multiplayer (MP) Search Same Capability as Beatmap Search"