I suspect you have the option, circled in image below set in the Projects settings
if so then you should also get a warning message on importing an image or video clip with a different Aspect Ratio to the project settings - selecting Do not adjust will maintain the whole image
However if you checked the option Don't show again then the last used setting will be remembered.
To turn the warnings back on click the Reactivate dialogs button in the Program settings, Options tab
John. I imported a folder with about 70 images. I did as you mentioned and I still have the same problem. I found under fx dropdown, I went to 'Section' / Free Proportions and I can adjust what is seen of the photo, BUT several photos always seem to revert back to where only a portion of the photo can be seen in the video! WHY??? (Not really liking this program right now!)
Can you post a screenshot of the timeline zoomed into to one of the images where you only see a portion of the photo - we need to clearly see the top bar of the image object.
Are the photos all from the same source and was this a digital camera, mobile phone or what?