So what i have come across in this short period of time ive been playing around with the devkit is that i forget so select the right level before placing all my items.
At the start I would just delete the items and replace it with the correct level selected, buuuuut!
If you select you desired level and mark all the wrong placed items and hit ctrl+x and then ctrl+v it will automaticly place them into the selected level.
This is the only way so fare ive managed to figure out how to do this.
If anybody got another solution please fire away! 
Hope this helps some 