OS: Windows 1903
Offsetting an image along the X axis, to the right,
with "Repeat edges pixels" enabled,
causes the bottom of the repeated edge pixels
to move up and anything below gets the Empty Area Background color.
The issue can be observed in the:
- Offset window, preview
- Main XnView MP window when "Apply to image" is checked
- And in the final image when the offset is applied (OK button)
A small side issue, there's a typo in: Repeat edges pixels
Remove the "s" after "edges".
Before: Repeat edges pixels
After: Repeat edge pixels
Effect:
Incorrect result of the Offset operation.
To reproduce:
1. Open an image
For example this one:
2. From the top menu, open: Image > Offset...
3. Now either:
- Enable "Apply to image" and move the Offset window so that the left side of the image is visible in the main XnView MP window.
Or enable "Preview" and resize the Offset window so that the preview is visible
4. In the "Empty Area" section at the bottom of the Offset window,
enable "Repeat edges pixels"
If the image has a black left edge, then change the "Empty Area" "Background color" to something other than black.
5. Drag the "Offset X" slider to the right, and release the mouse button or stop moving the mouse while dragging for a second so that the preview updates.
Actual behaviour (bug

Not all pixels to the left of the image are repeated, while dragging the "Offset X" slider to the right.
Until the slider reaches the right most position, then all of the left pixels have been repeated.
Screen recording
(the screen recordings (gif) below didn't play in the preview when this issue was written.
If they don't play after they have been posted either. Then open them in a new browser tab (only tested in chrome))
Less and less pixels are repeated the more the image is offset to the right.
The issue only occur when repeating the edge pixels to the left of the image.
It works fine when repeating the edge pixels, above, to the right and below the image.
And there are no visible issues when offsetting in any of the four directions, when the "Empty area" is set to either "Background color" or "Wrap image around".
Expected behaviour:
All of the pixels to the left of the image should be repeated.
Notes:
Increasing the value of the "Offset Y" slider, covers up the missing left side repeated pixels.
Screen recording