Putting a command button on the report may in fact be the culprit for that transient selection behavior. Older versions of Access made reports that were totally passive. The trend these days to allow "interactive" reports is relatively new. However, there should still be the upper-right-corner X to close the report.
As to opening a report in Dialog mode, I think that is what introduces the idea/ability of window resizing. BUT the question is, when you resize the window, does the report also resize, or is it more like a picture being cropped? Specifically, which setting are you using to tell the window it cannot be resized?