Steps to replicate the issue

1. Create a new page
2. Add an anchor to it (let's name it testanchor)
3. Now, add some text to the page
4. Highlight the text, and then click on the Link button in the tool bar
5. Now, go to Advanced
6. Type the name of the #anchor (on this test, type #testanchor)
7. Immediately press Enter.
   You will see the link is created. If you click on it and select Edit, when you open it, you can see the link was created with only part of the anchor name (on my test, it was created as #testancho).

If you wait a couple seconds before hitting enter, or use the mouse to save the link, the linking is created correctly (#testanchor)