JSC crashes on 64Bit machines

On 64bit machines JSC crashes erratically (in terms of when/where).

On debug builds it's always:
ASSERTION FAILED: offset == static_cast<int32_t>(offset)
(/home/tsenyk/qt/qtGit/src/3rdparty/javascriptcore/JavaScriptCore/assembler/X86Assembler.h:1603 static void QTJSC::X86Assembler::setRel32(void*, void*))

... but the when/where is still erratically.

I seams to happen more often in applications with more memory consume.

Also see:
http://developer.qt.nokia.com/forums/viewthread/13164/#72163
https://bugzilla.mozilla.org/show_bug.cgi?id=602333

The application I trigger the problem with:
http://gitorious.org/qtmediahub