These buttons should be vertical, instead of horizontal, because it's too difficult to move the mouse within the tiny space given (from top to bottom of the horizontal dropdown menu's region) when they are aligned horizontally. Also, it's more common and usable for items to be displayed vertically... you rarely see menus laid out horizontally like this.
The biggest culprit is Custom Command Buttons, of which I have many custom commands. The odd reordering of the custom commands are tedious enough (they should ideally be listed in order specified in the preferences, but that's perhaps for a different post).
Anyway, I've made a little demo video to show you what I mean:
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