I assume you are in a org-fc review, then navigate to a card different from the current one and use the suspend key binding (bound to
org-fc-review-suspend-card)?The behavior you're seeing is due to an oversight in the design of this function, because I didn't think that people would interact with other cards during the review.
This should not be hard to fix, instead of using the current card of the review session (which might be different from the card at point when using the suspend function), we can get the ID of the flashcard at point and remove that from the session.