I don't think it matters, but I think that the bracketed (sheet format size) might be a new addition to the standard sheet format properties die to a number of new standards introduced in Sw 2012. The answer might be searchable in the HELP files "custom properties" for 2012?
Thanks for the help Alexander. But I don't think it is a SW 2012 addition. It is the same in SW 2011 and older versions.