Hi
Once you have placed a clip on the timeline and then decide to select it there and review it Clip Preview (it would normally display in Sequence preview) you can only View it. As a consequence the Place button is no longer available. The button now says "View."
Selecting the same clip (or another clip) in the Clip Bin will automatically display it in Clip Preview in a similar way as above even though it is on the timeline.) As you have reselected it, VP considers it as new clip selection and displays it in the Clip Preview window where you can edit it, consequently the Place button is now displayed.
In short....If you want to edit clips in the Clip Preview screen and then place them on the timeline you must select them from the Clip Bin.
Nat