problem using parse launch and python element with properties

Hi, I have an error when using a python element with properties and parse_launch. If I create manually the element and set the properties it works fine but if I use it with gst-launch or parse_launch it gives this error:

sys:1: Warning: g_object_ref: assertion 'G_IS_OBJECT (object)' failed

(gst-launch-1.0:10662): GStreamer-CRITICAL **: 13:27:00.494: gst_bin_add: assertion 'GST_IS_ELEMENT (element)' failed ** ERROR:./grammar.y:646:gst_parse_perform_link: assertion failed: (GST_IS_ELEMENT (sink)) Aborted (core dumped)

You can find an example here: https://gitlab.com/skaboy/gst-python-tests in the test.py example plugin, just run test.sh to replicate the problem. I tested on latest stable release.