Tipsy nippers and the like usually fail on wing area, stall speed ect, and even if they did tick all the microlight box's they were registered as Group A before the microlight category was introduced. Another anomoly used to be the Slingsby T31m. It used to be classed as Group A or SLMG depending on how you registered it. Now they have all been reclassified as TMG's. You can keep your SEP rating valid by flying one with a TMG rating, but not if you only have a SLMG rating. I think you can count only 70 TMG hours towards CPL which is just as daft as there really isn't any difference in skill required to fly say a Grob 109 or C150.
SS