XnView Software

When I do manual Zoom In or Zoom Out in "Fit window to image" mode, window stretches or shrinks according to image size * zoom factor. But sometimes scrollbars appear. And when I stretch window size by mouse drag on 1 pixel more large, scroll bars disappear. Most often I see this on 51% zoom.
Also shoudn't manual Zoom Out twice change zoom factor from 100% to 50%? But it is 51%. Seems to be zoom factor float ceiling instead of rounding issue. If ceiling is necessary, maybe ceil of (ZoomFactor - 0.001) could help.

do you have a way to reproduce it?

I have explored this issue a little bit more and found, that this issue is actual only on Windows 7 with scaling 125%. But on Windows 7 with scaling 100% and on Windows 10 with scaling 125% all is OK.
So, XnView on Windows 7 with scaling 125% showing attached file "boot1080.gif" have scrollbars on single Zoom Out (100%->71%).
And XnView on Windows 7 with scaling 125% showing attached file "Vector_Video_Standards_3.PNG" have scrollbars on double Zoom Out (100%->51%).