something is happening,

I'm guessing the differences you are seeing is just down to the overhead of calling into C, doing (almost) nothing, and returning again.

From pp.c/5.18

/* Pattern matching */

PP(pp_study)
{
    dVAR; dSP; dPOPss;
    STRLEN len;

    (void)SvPV(sv, len);
    if (len == 0 || len > I32_MAX || !SvPOK(sv) || SvUTF8(sv) || SvVAL
+ID(sv)) {
    /* Historically, study was skipped in these cases. */
    RETPUSHNO;
    }

    /* Make study a no-op. It's no longer useful and its existence
       complicates matters elsewhere. */
    RETPUSHYES;
}
[download]