If Aldeth's captain-of-the-guard is addressed after the incriminating documents have been turned in, he continues to ask CHARNAME whether CHARNAME has uncovered any incriminating evidence. CHARNAME is forced to "admit" that he has yet to find any hard evidence, even though he already handed them over to the captain. This behavior continues even after the doppelgangers have been killed and the quest has been completed.
[Expected behavior] The captain-of-the-guard will recognize that he has already been given the incriminating evidence, or CHARNAME can at least lampshade the bug for everyone's amusement. :]