That is my experience as well, Hafeez. I find it absolutely frustrating to try to use the advanced features where rip rarely does what I want it to do. However, some people can really shine with the package because they have learned exactly what to do and what order to do them in. I have gotten better, but I reserve sheetmetal for only simple fabrications.
I am going to suggest you want to start your tubes from a revolve (1st feature) that you know you can "unbend". Next "bend back" and create your cuts. Be very aware on which side you want the feature to intersect and be consistent. As you you add new cuts, be sure to test the Unbend just on a temporary basis by deleting or undo-ing the feature. As long as it will unbend, it should be able to flat pattern as well. You might have to turn off the bend relief features in the options dialog.
Are you actually forming the tubes and welding the seams or is there another reason you want to see the flat pattern?