At the moment the following happens:

1) Create an issue and select a component, for example select Component A
2) Edit the issue and add another component, for example select Component B
3) Look at the Change History and see that the Original Value is blank and the new value is Component B

You can remove Component B during an edit operation (while leaving Component A selected) and notice that the Original Value is Component B and the New Value is blank.

This is because the change history stores and shows a "diff" of changes.

It would be easier to read if the full original and new values are shown. That is, in the example above, the original value would be Component A, and the new value would be Component A and Component B.