I wouldn't call this purely a production error, though it could be mitigated with a modicum of forethought by the production company. A nuisance of mine when listening to audiobooks is mispronunciation of terms or names, which is particularly common in fantasy books with fantasy names.
Two examples that readily come to mind are:
Roy Dotrice's reading of A Song of Ice and Fire, especially "Puh-Tyre" Baelish.
Red Dusk and the Morrow as read by Peter Owen. Generally a great narration, but there are a handful of German phrases and expressions which are pronounced in a very jaunty anglicised way, like "un-zeer dootshe Jenosen" instead of "unsere deutsche Genossen."