I have seen some orange caps that were very deformed in the stores. I only buy them when they are right in front of me so I can check them out, The 2 prongs that stick out can really be deformed also. I haven't seen the purple ones that another spoke of.
My orange cap occasionally will not be sealed when I start the vacuum. However, I find that if I hold it firmly in place for a few seconds and let the vacuum develop, it is soon well sealed.