I am not sure whether this is a bug but at this time timecode is not applied to bounced clips/regions (menu: Audio/Bounce selection). It also would be nice to have similar options as during mixdown (bitdept, naming etc) with bounce selection.
Perhaps change the title or first post so that it essentially means that any rendering of a new audio file yields BWF origin timecode. As it is now some bouncing will retain the timecode accurately, just not for some types of “content” (e.g. regions).