If you have a tuple and type "someTuple.", the content assist window pops up with the tuple members _1, _2, etc. However, if you type "someTuple._" and hit ctrl+space, the completions offered are "_root_" and all classes that begin with an underscore, but not the members _1, etc.
I would expect that the completion is the same as if you were to type "someTuple.", let the content assist window pop up, and then type "_". That is, it should only offer the type members _1, _2, and "__leftOfArrow", "__resultOfEnsuring".

val t2 = (2, 3)
t2._ //<-- completion here