crash in QTextCursor::setPosition(int pos, MoveMode m)

I don't know how to reproduce this crash but I have callstack

crash occur only on japan environment 

it crash here

http://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/text/qtextcursor.cpp#n83

as priv == nullptr

callstack:

Qt5Gui.dll!QTextCursorPrivate::QTextCursorPrivate(const QTextCursorPrivate & rhs) Line 83 C++

[Inline Frame] Qt5Gui.dll!QSharedDataPointer<QTextCursorPrivate>::clone() Line 240 C++

Qt5Gui.dll!QSharedDataPointer<QTextCursorPrivate>::detach_helper() Line 246 C++

[Inline Frame] Qt5Gui.dll!QSharedDataPointer<QTextCursorPrivate>::detach() Line 74 C++

[Inline Frame] Qt5Gui.dll!QSharedDataPointer<QTextCursorPrivate>::operator->() Line 77 C++

Qt5Gui.dll!QTextCursor::setPosition(int pos, QTextCursor::MoveMode m) Line 1151 C++

Qt5Widgets.dll!QWidgetTextControlPrivate::extendWordwiseSelection(int suggestedNewPosition, double mouseXPosition) Line 749 C++

problem can be fixed really easy but I don't understand why compiler choose non const method instead of const ????

It call from http://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/text/qtextcursor.cpp#n1151

NON CONST VARIANT
inline T *operator->() { detach(); return d; }

CONST VARIANT

inline const T *operator->() const { return d; }  

so it crash on clone

but then it still only check property priv  and then it release cloned object

{{void QTextCursor::setPosition(int pos, MoveMode m) }}

{{{ if (!d || !d->priv)}}

compiler MSVC 2015 64bit

any idea ????