Try changing the avatar, when you change it, instead of selecting a new image, click on the exisiting avatar, you'll see that the window will open in the same iframe and then you can open many nested windows. One of our clients reported this issue, so when we tested it here on lithosphere, we got it here as well. Steps:
Edit avatar by hovering on you avatar > choose another avatar > in pop-up, click From the community > Click on your Current avatar, you’ll notice that the nested windows open in an iframe. Attached is the Screen Shot.