I am currently using Adobe Acrobat Pro 9. Whenever I use the crop tool (or the TouchUp Object tool), the program does not allow me to make a specific selection (with the crop tool) or a specific placement (TouchUp Object tool). Instead, it snaps to an invisible grid/jumps in increments!
This wasn't always the case... I tend to use hotkeys/shortcuts, so it could have been an erroneous keystroke which led to my current situation, but I can't seem to find the specific setting relating to this issue.