On 3.8.8, the start menu always opens on the primary monitor (regardless of where keyboard focus or the mouse is currently located) if you have enhanced classic taskbar off. This behavior also occurs if you click the start button on a secondary taskbar.
Expected Behaviour:
The start menu should open on the currently active monitor (determined by keyboard focus or mouse position, whichever is most recent) when the start menu is opened (either via the Start Button, or via the keyboard META key).