Just for your info: The dropdown menu uses a few adjustment mechanisms. First of all, the dropdown is linked to a button and will not automatically inherit the width of the button that opens the dropdown ... content of the dropdown might be wider or narrower than the button ... The menu does automatically expand to "at least" the width of the button, but it will sometimes expand to wider than the width of the button. Also, dropdown menu items have different paddings and font-sizes from the top-level item ... From just viewing your screenshot, I can't see anything specifically wrong. A menu could expand to be wider than the top-level items.
I checked here from both Chrome and Firefox, and it looks like the below. It may adjust itself on FIRST mouse-hover, because this is the first time the menu can measure it's own width (we can't measure width of hidden menu items). This could perhaps have been implemented better, but in most cases, it won't happen and/or nobody would notice.
I'm not sure how you get that screenshot, as it's different from mine, but none of them are essentially wrong. Perhaps you have some custom zoom level in browser that is affecting fonts.