In the image editor if Width < Height you can't select the entire image.
<img src="http://i.imgur.com/5chsL.png" border="0">
If Width > Height you can select through the canvas.
<img src="http://i.imgur.com/7cTEx.png" border="0">
Here is a sample: SampleBug.capx
Sorry if it has already been reported.
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Thanks, should be fixed in the next build.