Since you are working on the new Select component maybe not much of a priority, but I guess make sure the new one avoids these problems?
If you enable Custom Values and type one in, you would expect that just hitting enter would accept the value just as it works if the item was in the list and you used type-ahead. Instead you are required to click the item that is generated in the drop down.
Speaking of that drop down, it is highlighted with a light blue background and a white foreground making it almost unreadable.
I tried to figure out some CSS to fix issue 2 but was unsuccessful.
Edit: I see the problem 2 is actually not related to custom items but happens all the time. When you hover over an item already selected, the highlight turns light blue but the text stays white. It is just more impactful with a customer value.