What is the 'main window' in your description? Is that the timeline layout?
I'm guessing that you are going back and forth between the timeline and the FX editors.
I'm not able to reproduce the issue based on your description, would you give me more details please
The main window is the timeline layout, I have a video of the issue happening but was unable to upload it to the forum. I have just updated to the latest version and confirm it still happens. Whilst in the edit dialogue where I have selected an overlay image, if I try to move the image and accidentally select the background it deselects the image I was editing. The only way to get back to editing the image is exit to the timeline and re-select it.