Understanding ambiguous datetimes when going from UTC to local

[MC-DeltaT]

I notice that all the functionality in Timex for conversion from UTC time to a specific timezone time seem to have the possibility of returning an ambiguous datetime (Timex.AmbiguousDateTime).

I am no expert on timezones, but I would have thought that going from UTC to a local time is always unambiguous (it is going the other way from local time to UTC that may be ambiguous, e.g. with DST). I.e. at a specific point in time, a given timezone has exactly 1 associated local time. Evidently this is not the case though? I'm wondering if anyone could shed some light as to why this is so.

I have seen the 2 cases of ambiguity in the Timex.AmbiguousDateTime docs, but I'm unsure if they apply here.
Case 1 definitely does not apply (this concerns going from local time to UTC).
Case 2 seems like it might be the reason, but I don't understand how "more than one zone applies to a given date and time" if we have already specified and fixed the timezone. If we say the timezone is Asia/Taipei, surely this leaves no room for ambiguity?