While every language is rife with variation, some variants can only be adjudged to be the wayward product of a kind of tone deafness or linguistic solipsism, conditioned more often than not by an unconscious adherence to the orthographic representation of a word. To cite an example from my own linguistic milieu, I have a friend who consistently mispronounced the first name of another friend even though he heard me pronounce it correctly on numerous occasions. This was a case where the spelling -ai- of the Finnish name Raimo gave rise to the vowel in English rain instead of the vowel of line. Eventually, the insistence of the letter yielded to the aural dominance of the sound, and the name is now pronounced correctly.
But this sort of linguistic solipsism can also persist uncorrected regardless of numerous audible examples to the contrary and in the absence of spelling influence. A prominent case is the speech of President Barack Obama, who consistently pronounces Taliban with a flat first vowel, a palatalized liquid, and a broad final vowel, in what seems like an attempt to imitate a fancied foreign model taken to be “authentic.” Perversely, Afghanistan in his speech is rendered with uniformly flat A‘s, but Pakistan with uniformly broad A‘s. (The latter pronunciation is doubtless an imitation of Pakistani English.) He also vacillates between pronouncing Copenhagen correctly and incorrectly, i. e., with a broad A instead of the traditional –ay– diphthong of rain––yet another instance of faux authenticity (not unknown in the speech of miscellaneous other Americans as well).
At bottom, this kind of idiosyncratic variation is a sign of linguistic insecurity. And no wonder: confronted with having publicly to render the Babel of foreign names and their variant phonetic forms in English, anyone––but especially a monolingual speaker––can easily come a cropper.