qtglvideosink color convertion

Official QtGstreamer documentation says "qtglvideosink uses OpenGL/OpenGLES and supports hardware colorspace conversion and color balance". gst-inspect says that "qtglvideosink has capabilities: video/x-raw-rgb and video/x-raw-yuv".

I want to display video decoded by TIViddec2 gstreamer element. It has following 'src' capabilities: video/x-raw-yuv (format UYVY) and video/x-raw-yuv (format NV12).
If I link qtglvideosink and TIViddec2 directly then video isn't shown. If I insert between qtglvideosink and TIViddec2 ffmpegcolorspace element then video is shown.

Why qtglvideosink don't convert colorspace?
Do I do something wrong or it is bug of qtglvideosink?

Sounds like you want to ask this on a GStreamer forum.

Cheers,
_