If you have enabled the option limitWidth for the back-end theme, the #container will jump left and right in operating systems or browsers with fixed scrollbars, when you navigate between a page that requires vertical scrolling and one that does not.
This could be fixed by
body {
overflow-y:scroll;
}
(also happens in Contao 3 and presumably Contao 4.3)
Eventually added in c169750a23e3fb5cf1cbe19143740e11be5b8a6e.
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Eventually added in c169750a23e3fb5cf1cbe19143740e11be5b8a6e.