I've been having ongoing problems w the rear deck latch on my 08 Prius. Initially it took extra pressure to engage the latch, then began to stick in the locked position with the door up, so I couldn't shut and latch the door. I tried lubricating the latch to no avail. I finally replaced the latch and striker both and it's still a problem with the "door open" light indicator on even with all the doors locked. Tried stacking shims behind the striker to more fully engage the latch without success. I do notice when I manually operate the latch, the "door open" light doesn't go out until the latch rotates another 30 degrees or so beyond simply engaging the striker, so for whatever reason, that latch is not fully rotating (it is new).
This thread: Touch switch won't open liftback has some interesting information. I suspect you need to disassemble the switch mechanism and clean it out, possibly replace the switch. Hope that helps.
