I don't have reaper in front of me right now, so I'm going off memory, but:
If you select and then right click on the items you are having trouble with, which is likely all of them, you will see the "item properties" choice. Click on that and choose to edit them "En Masse" or whatever it says. You will see a drop down to change the items position to either move with the tempo of the song or not, and some other options that escape me right now as well.