the first issue is probably a layering problem, make sure the button texture is attached to something on a higher frame level than whatever the background is.
https://wow.gamepedia.com/Widget_API#LayeredRegion
the second issue is most likely sub-pixel errors, when relying on single pixel accuracy you'll need to "pad" your dimensions and/or positions to account for floating point errors.
increase the frame size by 0.1 px or shift it a similar amount in both directions.