this is what you see now when you have the wrong size in a free.

gistfile1.txt

Address 0x7EF34B0 len 133117112 not defined:
Uninitialised value at 0x7EF34C4
==20692==  Address 0x7ef34b0 is 0 bytes inside a block of size 32 alloc'd
==20692==    at 0x4C2DB9D: malloc (vg_replace_malloc.c:299)
==20692==    by 0x50428CB: MVM_malloc (alloc.h:2)
==20692==    by 0x50434A0: MVM_fixed_size_alloc (fixedsizealloc.c:178)
==20692==    by 0x50DD6ED: MVM_string_decodestream_add_chars (decode_stream.c:55)
==20692==    by 0x50E2907: MVM_string_utf8_decodestream (utf8.c:431)
==20692==    by 0x50DD98C: run_decode (decode_stream.c:115)
==20692==    by 0x50DDA93: reached_eof (decode_stream.c:146)
==20692==    by 0x50DE780: MVM_string_decodestream_get_all (decode_stream.c:484)
==20692==    by 0x509F68F: MVM_decoder_take_all_chars (Decoder.c:234)
==20692==    by 0x501B418: MVM_interp_run (interp.c:5127)
==20692==    by 0x5110EA7: MVM_vm_run_file (moar.c:387)
==20692==    by 0x4014D1: main (main.c:255)
MoarVM panic: Fixed size allocator: wrong size in free