This is a rather minor bug. It might better be called a "feature request," but I would think it is an obviously missing feature.
When the editor is in split window mode, one side of the editor has a fixed width or height (depending on orientation) and the other side has a resizable width or height. When the editor window is resized, only one of the sides resizes and it is impossible to move the divider to reapportion the sizes of the two sides.
Most similar UIs use a movable splitter for the split window feature.


