When I open the graphical editor, it seems that the editor used is the GMF one.
We have noticed some conflicts between these two graphical editors : we need to look deeper into GMF code to analyze its origin. While waiting for a fix on this issue, you should disabled the GMF Example feature which should prevent this to happen. [Fixed in 0.8.0M4]
Icons are not visible in my diagram
This is related to the bug 209802 which also depends on the bug 211851. You should turn antialias OFF until this issue is fixed : Window > Preferences > Ecore Tools Diagram > uncheck the 'Enable antialiasing' option