valgrinding 8.4 crash

mig@ari:~/DEVEL/tcl-core/core-8-4/unix$ valgrind ./tclsh
==23664== Memcheck, a memory error detector
==23664== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==23664== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==23664== Command: ./tclsh
==23664== 
% proc {} x {$x}
% []
==23664== Invalid write of size 1
==23664==    at 0x41D2F9: Tcl_ConvertCountedElement (tclUtil.c:742)
==23664==    by 0x4167BC: TclObjInterpProc (tclProc.c:1159)
==23664==    by 0x42B26F: TclEvalObjvInternal (tclBasic.c:3260)
==23664==    by 0x46229F: TclExecuteByteCode (tclExecute.c:1589)
==23664==    by 0x46149A: TclCompEvalObj (tclExecute.c:1105)
==23664==    by 0x42C9DE: Tcl_EvalObjEx (tclBasic.c:5241)
==23664==    by 0x47392E: Tcl_RecordAndEvalObj (tclHistory.c:140)
==23664==    by 0x40FE46: Tcl_Main (tclMain.c:391)
==23664==    by 0x40F61A: main (tclAppInit.c:88)
==23664==  Address 0x574b432 is 0 bytes after a block of size 2 alloc'd
==23664==    at 0x4C2815C: malloc (vg_replace_malloc.c:236)
==23664==    by 0x4BA2C5: TclpAlloc (tclAlloc.c:687)
==23664==    by 0x430D5C: Tcl_Alloc (tclCkalloc.c:1009)
==23664==    by 0x41679A: TclObjInterpProc (tclProc.c:1158)
==23664==    by 0x42B26F: TclEvalObjvInternal (tclBasic.c:3260)
==23664==    by 0x46229F: TclExecuteByteCode (tclExecute.c:1589)
==23664==    by 0x46149A: TclCompEvalObj (tclExecute.c:1105)
==23664==    by 0x42C9DE: Tcl_EvalObjEx (tclBasic.c:5241)
==23664==    by 0x47392E: Tcl_RecordAndEvalObj (tclHistory.c:140)
==23664==    by 0x40FE46: Tcl_Main (tclMain.c:391)
==23664==    by 0x40F61A: main (tclAppInit.c:88)
==23664== 
wrong # args: should be "{} x"