if you create ill-named database (such as "admin sha" or "*") you can't rmeove them.

How to do it :
use admin sha
db.dropDatabase()

you get :
"errmsg" : "

{ assertion: \"invalid db name: admin sha\", assertionCode: 13280, errmsg: \"db assertion failure\", ok: 0.0 }

"

if you try to remove it with a command :
db.runCommand(

{dropDatabase : "admin sha"}

)

{ "ok" : 0, "errmsg" : "invalid params" }

Creating such ill-named database should be forbidden (spaces in the name) but it should be possible to remove them.