Parkway Properties Inc. on Sept. 22 announced plans to spend $475 million to buy a portfolio that has 22 office buildings in six states, most notably, three Class A towers in the Tampa Bay area. What wasn’t announced, however, is that hidden in that portfolio are three buildings in Orlando’s Central Florida Research Park, properties that the Orlando-based real estate investment trust (NYSE: PKY) doesn’t plan to hold onto, real estate sources said. The three Research Park properties are the…