I try run example from videomixer2 :

gst-launch-0.10 \
  videotestsrc pattern=1 ! \
  video/x-raw-yuv,format=\(fourcc\)AYUV,framerate=\(fraction\)10/1,width=100,height=100 ! \
  videobox border-alpha=0 top=-70 bottom=-70 right=-220 ! \
  videomixer2 name=mix sink_0::alpha=0.7 sink_1::alpha=0.5 ! \
  ffmpegcolorspace ! xvimagesink \
  videotestsrc ! \
  video/x-raw-yuv,format=\(fourcc\)AYUV,framerate=\(fraction\)5/1,width=320,height=240 ! mix.

It working, i see picture with colored lines and rectangle with noise; at the same time process gst-launch eat memory. memory consumption grows untill oom killer will not  kill the process;

This is especially notable if the output video to fakesink. memory  filled very quickly (on my system with 2 gigabytes of memory it takes a few minutes)

If i replace videomixer2 by videomixer everything  works well and memory consumtion remains constant.