Line artifact when resizing layer

[Estoc]

When I select something then stretch it, a white line appears at the edge.  The video demonstrates this.  Why does this happen and how can this be fixed?  Photoshop does not do this to my knowledge.  

Edit:  when I stretch the selection slightly to the left to try and get rid of the white artifact, the artifact becomes darker instead and remains a visible line.

[HVDB Photography]

I think you shifted the selection to the right which reveals the (white) canvas !

 

[Estoc]

I've tried the procedure numerous times,   I simply make a selection and without moving the selection, select the hotkey to resize, and do like so.  I do not think that it is the case that I am shifting it by accident to the right.

[GarryP]

When you stretch the pixels during the resize, the software has to create the new pixels from what it knows about the originals.
Unfortunately, it does this by ‘sharing’ the amount of colour that was in the original pixels amongst the new pixels.
Think of it like stretching a thin sheet of rubber, where the rubber becomes lighter the further you stretch it because the bits of the material containing the coloured pigment become further apart, or more diffuse (I'm not a materials scientist so this might not be exactly what happens, but the analogy works for me).
One basic method to counteract this is to duplicate the stretched layer a few times and merge the duplicates down into each other.
Another method is to use the Mesh Warp tool to stretch the layer instead.

Edited February 23, 2020 by GarryP
Added 'disclaimer'.

[Estoc]

Fixed the issue, the painting layer had a bit of transparency to it,  so I merged it with a blank white layer, and redid the operation + moved it slightly to the left.  Got rid of the white line.

[GarryP]

In case anyone is interested, here’s a short video showing how to do it with the Mesh Warp Tool.
It doesn’t work perfectly for all backgrounds but it’s good enough for a lot of quick jobs.