os: Ubuntu 10.04
gtreamer version: 0.10.29 (from gstreamer-dev ppa)
Pitivi: 0.13.4


how to reproduce:

1. import a jpg file
2. put it in time line
3. try to make it semi-trasparent


I think the bug is gstreamer-related because other user say to me that pitivi with original ubuntu gstreamer package worked fine. 

But I'm not sure.

STRANGELY, The transparence problem seems to disappears if I render the project, event in pitivi preview, but actually it dont desappears because transparency works bad (I cannot tune it)


Additionally, I receive some errors from pitivi, when i put a png or gif in the timeline:

Problema:GStreamer ha incontrato un errore generale di stream.
Informazioni supplementari:gstqueue.c(1212): gst_queue_loop (): /GstPipeline:pipeline0/GstBin:bin0/GnlComposition:gnlcomposition0/GnlSource:gnlsource: PictureFileSourceFactory1/GstBin:bin2/GstQueue:internal-queue:
streaming task paused, reason not-negotiated (-4)


After this, I receive errors even with jpeg:

Problema:GStreamer ha incontrato un errore generale di stream.
Informazioni supplementari:gstbasesrc.c(2543): gst_base_src_loop (): /GstPipeline:pipeline0/GstBin:bin0/GnlComposition:gnlcomposition0/GnlSource:gnlsource: VideoTestSourceFactory5/GstBin:bin8/GstVideoTestSrc:videotestsrc1:
streaming task paused, reason not-linked (-1)

And the preview doesn't work at all.

Thank you.