Hello,
This issue concern at least both versions : 2.4 + 2.6
About multikey indexes : not sure but it seems to me that the last sentence is bad on the bottom of the following document page :
http://docs.mongodb.org/manual/core/index-multikey/

Current sentence :
"This would select the document, that contains the following document in the comments.text array:"

Sentence maybe more true :
"This would select the document, that contains the following SUB-document in the comments array:"
> "following document" becomes "following sub-document"
> "comment.text" becomes "comments"