Do You Need to Subpoena A Testifying Expert for Deposition?

 Magistrate Judge Brown says yep:

Although it is true that Defendant had the right to depose Dinsmore as a testifying witness under rule 26(b)(4), Defendant may have confused this right with a party's non-existent duty to compel a nonparty deponent's attendance without a subpoena. Defendant's motion for sanctions is groundless.

This is unusual in that the parties typically agree to make their testifying experts available for deposition without formal subpoena.

But nothing in this case is typical, is it?