Looking through the docs for Bootstrap 4, I came across this oddity:
Right now, in Chrome v48, the select element renders a lot smaller in height compared to other input elements.
In comparison, Bootstrap 3, doesn't have this problem:
Is this a conscious choice or due to it still being alpha?
Yep on chrome select has a size of 20 while the other input fields are with a size of 24 (consider box model)
I don't know if this was a design choice or a fluke but on the style itself select is with a height of 34px and inputs with 38px.
If you want you can probably overwrite the style and get the desired behaviour.