I can now reproduce your problem using your first code snippet, both on 5.8.2 and 5.8.1. The code dies here, in pad.c (Perl_pad_undef()):

    /* detach any '&' anon children in the pad; if afterwards they
     * are still live, fix up their CvOUTSIDEs to point to our outside
+,
     * bypassing us. */
    /* XXX DAPM for efficiency, we should only do this if we know we h
+ave
     * children, or integrate this loop with general cleanup */

    if (!PL_dirty) { /* don't bother during global destruction */
    CV *outercv = CvOUTSIDE(cv);
    U32 seq = CvOUTSIDE_SEQ(cv);
    AV *comppad_name = (AV*)AvARRAY(padlist)[0];
    SV **namepad = AvARRAY(comppad_name);
    AV *comppad = (AV*)AvARRAY(padlist)[1];
    SV **curpad = AvARRAY(comppad);
    for (ix = AvFILLp(comppad_name); ix > 0; ix--) {
        SV *namesv = namepad[ix];
        if (namesv && namesv != &PL_sv_undef  /* DIES HERE */
        && *SvPVX(namesv) == '&')
        {
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This code is identical in both 5.8.1 and 5.8.2. Now I need to check 5.8.0 to see what has changed.

UPDATE: The pad.c file (and associated functions) is new in 5.8.1... So it won't be a question of doing a simple diff :-(. I guess that this is one for the perl5-porters list...

Michael