UPDATE:
As I have since found out, it isn't actually a buggy choice of crew mate, but the dialogue system simply displays the wrong crew members, but runs the skill check against the correct one, i.e. in this case runs it against the actual helmsman, even though the dialogue might say that the gunner were at the wheel at the time.
So still nonsensical, but at least the skill check itself can reliably be passed if the actual professional is, well, professional enough.
Encountered Behaviour:
Game chooses displays wrong crew member for skill check to navigate the "Fanged Strait"-reef; instead of "Seasoned Helmsman" or "Expert Navigator", the game chooses a cannoneer for crying out loud(!) to man the wheel while navigating this reef, even though said cannoneer is stationed at the cannons, and the helm is manned by said expert helmsman!
Both dialogue comments as well as "navigate safely through the reef"-skill checks are therefore performed by a completely unqualified and unassigned crew member for no apparent reason whatsoever -- subsequently, the skill check is failed, despite having highly trained experts both at the helm/wheel as well as on navigation duty.
Expected Behaviour:
Game should never choose crew members for stations they aren't even assigned too nor in the least bit qualified for, at the very least not as long as there are already much more qualified people assigned to the much more logical crew stations for any given skill check -- i.e. the "Navigate the reef"-skill check should have been either the helmsman's or navigator's task, but never ever ever the cannoneer's!
Reproducibility:
100%
Game always chooses Coin-Counter Foeldas (Cannoneer assigned at Cannons) over Birta (Seasoned Helmsman assigned at Helm) as well as over Worthless Idiot (Expert Navigator assigned at Navigation).
Severity of Bug:
Not a plot stopper, but very stupid and annoying to "lose a skill check" because the game itself sabotages said check by being retarded, choosing a gunner to navigate through a reef, instead of the highly trained expert personnel already available.