Steps to reproduce:

1. Copy a URL from somewhere.

2. Open a page in VisualEditor and select some text.

3. Quickly press Command-K (to make a link), then Command-V (to paste in your URL), and Return (to close the dialog box).

4. Notice that VisualEditor made an internal link to your selected text, rather than an external link to the URL that you pasted in.

Workaround:

1. Copy a URL from somewhere.

2. Open a page in VisualEditor and select some text.

3. Press Command-K (to make a link).

4. Count to three, then press Command-V (to paste in your URL).

5. Count to three, then press Return (to close the dialog box).

I use this particular workflow a lot. I don't expect to have to slow down my typing on such a basic task.