Ugh, I have had several work situations over the years where I have wanted to scream, "Can you please forget I know how to do that job??"
Sometimes it's when you get promoted or transferred into a different position and the old, undesirable department wants to borrow you "just today, because we're really stuck." (It's never just today, they will ask again and again and again).
In my case it was when I wasn't getting full time work in Position A, so I took the initiative to also train for the less desirable Position B, as a separate job within the same company, to supplement my income. Then, when I finally had more stability and hours with Position A, I quit Position B. But then the manager of B department was always "arranging" with the manager at "A" to "borrow" me "because so-and-so is sick and we're really stuck." Nobody else from Department A was asked to do this, because they didn't have the misfortune of knowing how to do the job in Department B.
The other thing that happened to me when I worked both jobs was that Position A slashed my hours even more, with "Oh, we gave more hours to Colleague John than you, because you're getting all those hours over in B so it's fair to even it up." No, it's not fair, because I took the initiative to apply for and take on Position B, and John did not.