Well, I tried it and didn't have the problem. Perhaps you can try again. I had an individual's record open to do this--might have made a difference, I don't know. I went to Build/Template-Event New I entered the following in their boxes: Type: Census Med: 1930 Long: Census 1930 DEDCOM: Ce1930 LDS: F Detail#A: HeadAge/Sex DetailB: Details Year Min 1928 Year Max 1931
Under definition, I simply put: "information from the 1930 census." I didn't fill in the source info yet, but can pretty much copy that from the 1920 census info.
Then when I went back to add an event to the individual record, Census 1930 was on the list of extended events.