Premise: I have v2.1.5 running on both Windows XP and Windows 8.
Issue: scaling (involved keys = o / Alt+o / Alt+Shift+o) is working properly on XP, but not on Windows 8... and I'd bet this is also a Vista / Windows 7 issue.
Specifically, when zooming beyond the fit-level (thus working with frames theoretically larger than the actual display's), the frame gets cropped but not properly: theoretically, the whole screen should be used, but instead, the more I zoom further the thicker an "intruder" black-bar rise from the bottom. This happens when running on dual monitor. When in single monitor it's even worse: an additional black-bar also rise from the right.
Under these circumstances, switching trough crop and aspect ratios produce additional crazy results. By the way, observing how the image changes (size/aspect) it SEEMS like cropping actually takes place BEFORE the aspect-ratio-resizing (while theoretically the later should occur first).
As I said, none of these problems displays on XP, so... I'm not an expert here... but it FEELS like the routine adapting the scaled-viewport has partially lost compatibility, possibly querying the system with parameters that are no longer supported on newer versions of Windows, or the same parameters are now insufficient.