EDIT: After more testing, it in fact user can resize both width and height but only height is changed in the main window (vertical resizing only), but then it makes embedded ui objects like the keyboard to still resize horizontally and vertically (either ignoring constraints inside editor or not allowing main window to resize width when it could) and then clip to container window which in turns hides contained elements like the right arrow. This is only happening if user resizes diagonally and to the right direction resulting in both width and height being resized and width being larger.
If user constrains the resize to only one degree of freedom or if diagonally ; goes to the left, then only height is controlled and it works as expected (because width shrinking is limited to a minimum window width size).
It should probably either disable width resizing inside the window editor or enable main window container to resize horizontally as well.
Hope that helps