Hi milkwaif, possibly something in your edited SidePane.htm causes the width of the side pane to change a little which in turn triggers a resize of the viewport area. That then triggers viewports getting arranged and probably solves the problem.

One question about the flickering - when it does happen if you then switch to split view to get rid of it, does it ever happen again within that same session like if you open the same file up again using File > Open this time instead of double-clicking it in Explorer?

- Michael