I travel with the mounting plate in place and have never had any problem.
+1
However, I have often loosened the mount to get at my stem bolts to position my handlebars during packing. This is not a problem. To protect the cable on Ortlieb handlebar bag mounts do not tighten the retaining bolts too tight (just snug). It does not take much pressure to have enough friction to hold the mount securely. The cable does not need to be mashed. I have removed mine several times when switching between bikes, and still have the original cable (about 5 years old). I am really sold on Ortlieb products.
Ortlieb bar bags are waterproof as are their panniers. This is a medium Classic. My camera goes in the orange case.

Wayne, at The Touring Store has the Classic $102 right now. He provides excellent service and is great to do business with. If you decide on Ortlieb, I'd also recommend getting the map case. It is very handy, and waterproof.
http://www.thetouringstore.com/index.htm