V. 1.05

When you are in ship designer editing a ship and press on the tech progress bar in the top left corner, you can no longer exit the ship designer by pressing "Cancel" button. The technology window opens "behind" the designer interface and the popup asking if "you are sure you want to cancel editing the ship without making changes" is behind there also. Only way out is to save changes to some ship to get out of this screen shuffle, and once you are out - there are your cancel editor popups in a stack, as many of them as you've created by trying to exit the designer.

A similar issue can arise in the technology screen with the mining techs that require drones. They also have a "spend drones?" popup that can appear behind the research interface and block you from exiting the screen. I'm less sure of exact the sequence of actions that can lead to it.