Plot Styles .ctb not showing in dropdown. DraftSight vs.1R3.1 x64, WIN7

Hello all,

I have a plot style table with .ctb styles and have pointed to the right folder location but when I go to choose a style I only get .stb styles as an option. This did not happen in previous versions, has something changed? Can anyone tell me what I am doing wrong here? Thank in advance. B