Which slide quality do you use?
I'm using the High 24-bit setting.
I think what you are seeing is artifacting after the 9 slice scaling kicks in. It will indeed skew the images.
I think if I were in your shoes, I'd simply forgo the text bit and include it as part of the image itself. Then simply size the image accordingly.
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Yea I'm not sure why I didn't think of doing that before.