<img src="https://dl.dropboxusercontent.com/u/66127489/images/TileSet.jpg" border="0">
Capx File
Change Letterbox Scale to Letterbox Scale Integer.
In mobile export work with fullscreen. Letterbox Scale Integer not best for mobile.
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This is always going to happen when you don't use Letterbox Integer Scale, it's not a bug. You could try turning pixel rounding on to see if that helps.
Closing as not a bug. You have to use letterbox integer scale. To avoid wasting space on mobile screens you'll need to choose the window size carefully so it can scale up by an integer factor and still closely fit the window size.