I would personally replace the 20A OCPD with a 15A OCPD and be done with it. The weakest link ( without the exceptions to the rule ) would be the best choice in this case. Since the NEC tells us the ampacity of the NMC based on 60 degree's as I believe I-Wire stated.....as well as the following:
(D) Small Conductors. Unless specifically permitted in
240.4(E) or 240.4(G), the overcurrent protection shall not
exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,
and 30 amperes for 10 AWG copper; or 15 amperes for
12 AWG and 25 amperes for 10 AWG aluminum and
copper-clad aluminum after any correction factors for
ambient temperature and number of conductors have
been applied.
I guess unsafe brings in the fact of yes it is 14AWG,,,and if you use 310.16 we can see the actual ampacity of the 14 AWG....but alas we know we can only use the 60 degree column....unsafe...well the properly sized OCPD will make it SAFER than it would be so thats of optimum word i guess.
The majority of times we run conduits to " the other execptions " allowed and are able to use the total ampacity for adjustment and what have you.
P.S. Just broke my femur last week and just now getting to my computer again.....feeling loopy so hope this types out ok...