demonstration pango-sharp bug. This bug is memory leak. I've used gtk-sharp 2.99 version but this problem appears in 2.12 version too.

After git clone you must extract Debug.tar to Simple_GTK/bin/Debug folder

video you can download here https://www.dropbox.com/s/bsua6dpt6y7lsm2/VID_20180707_223544.mp4?dl=0