I am glad you confirmed that, since as I was playing with X3 I could not remember "for sure" where they opened! I figured it would be better to bump the thread than make that assumption.
I typically open, move, do my thing, close... so reviewing this thread was the first time I think I have ever "just opened" three at once (and they are stacked when doing that).
Edit: From a parent/child perspective it makes sense for this behavior, since Windows will open a new window based on the last child creation (typically tiled format). Remembering a particular plugin once released (and worse by plugin location - say three of the same plugin, but on different tracks) may be a bit more difficult than initially meets the eye. Once closed/released, that data is "gone" unless specifically stored "somewhere."