crash with QGraphicsDropShadowEffect and OpenGl viewport

My program crash with QGraphicsDropShadowEffect and OpenGl viewport, trying to apply it to QGraphicsSimpleTextItem

it seems because
Q_ASSERT(img.format() == QImage::Format_ARGB32_Premultiplied || img.format() == QImage::Format_RGB32);
in expblur QPixmapFilter.cpp

since QGLPixmapDropShadowFilter::processGL
makes image in Format_Indexed8 format

without OpenGl vievport effects works fine