Which application did you use to edit your image? Are you running Acrobat on Windows or a Mac?
Based on your screenshots, I would assume that this is a bug. Here is what I would do to find out what happened: Acrobat's Object Inspector can tell you information about the size and resolution of images. Select Tools>Print Production>Output Preview and then select "Object Inspector" in the "Preview" section. When you now click on the image in the original document and capture the information and compare with the data from the modified version, do you see a difference? If not, you should be able to resize the image using Tools>Content>Edit Object
If you need just modify one dimensions (vs. a proportional scaling of the whole image), then hold down the shift key while you drag one of the corners.
Karl Heinz Kremer
PDF Acrobatics Without a Net
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