Also when I double click an image in my project that is mysteriously not listed in the images folder, the Image Properties dialog shows the file path correctly at the top with my image file and when I display the contents of that very same folder on the left of the dialog, it is not there. All of my images are .png, .gif or .jpg. There is nothing in the filenames that should be confusing the issue. i have been maintaining this project for 3 years and never had anything like this happen.
If RoboHelp allowed you to replace the image and it were a different size, you could have problems in the existing topics. I suspect that is why it is not allowed to replace it in that way.
As far as "missing" images are concerned, try renaming the folder to say Images2. They will likely all appear and then you can revert the name.
See www.grainge.org for RoboHelp and Authoring tips
Indeed!! Thank you
Could you please report this as a bug to Adobe? It'd be nice to have another voice report this officially.