yet if you have a piggy back PPL and no IMC or IR on the JAA PPL then you are limited to "in sight of the surface"....
Actually that's only true for a UK-issued "JAR-FCL compliant" PPL. Other "JAR-FCL compliant" PPLs may not have that same restriction.
But essentially, yes, all the limits of the underlying license will apply to your piggyback license as well.