When issue #1514 was fixed, the import image dialog was forgotten, probably because it was introduced in Gazebo 5 and all other dialogs were fixed from Gazebo 4.1. See this question.
It was recently reported on the issue that the problem persists when trying to save the world, but I wasn't able to reproduce that. Could it be that the user is using an old Gazebo 5 build?
I also fixed a crash I just found when trying to save an empty building on Gazebo5.