Some videos, particularly in the .mkv format, will sometimes have a different aspect ratio between the file ratio (when it is not resized from the DVD source when ripped) and the display ratio it's meant to be seen in.
VLC player always used to take snapshots in the display ratio, but lately it appears that it's using the aspect ratio. So, let's say you have a video that is supposed to display in 4:3. The video is 720x480 because of that's how it actually is formatted on the source DVD (however, it's very smooshy), but it *should* display at 720x540.
Also, if you manually change the aspect ratio or crop a video with the VLC controls, it used to snapshot what was actually displayed in your VLC window, rather than the original file.
VLC player didn't used to have this issue. Also, 2.1.5 is far too buggy to downgrade to (it doesn't even exit properly). This is certainly the lesser of two evils.