Just to wrap this one up.... It appears that eval_pv (and eval_sv) return a mortal SV* that must be cleaned up by "topping and tailing" the call to eval_pv with:

         ENTER;
         SAVETMPS;
         value = (eval_pv("1;", TRUE));
         FREETMPS;
         LEAVE;
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The assignment SV* value is required, else errors about freeing unreferenced value are generated. Shaun.