Required two monitors to replicate.
<img src="http://img197.imageshack.us/img197/7489/clipboard01jw.jpg" border="0" />
Steps to reproduce:
1. Try to right click to modify polygons in "Edit image dialog" in your secondary monitor
The right click menu don't appear
The right click menu should appear
If you move the window to your primary monitor, the menu will show after the click just fine.
Operating system & service pack:
Construct 2 version: