Google Maps seems to think that MD 2 SB follows Hughes the whole way from Light to Hanover, but it appears that
traffic can only turn right at Charles and thus it is legally impossible to continue straight on Hughes across Charles (not that that stops people from trying, I imagine...). Combined with the fact the Hughes is rather narrow between Light & Charles (but a more standard city street width between Charles & Hanover), the Lee-Charles-Hughes routing would make more sense as others have suggested.
Another possible hint supporting the Lee-Charles-Hughes routing...looking at the HLR pdf that 74/171 linked to, the "route number" listed for MD 2 NB's intersection with E Hughes St is "MU 6145" (presumably some internal city designation...it's on page 24 of the HLR pdf for anyone interested). I would think that route number would instead show as MD 2 if SB did in fact follow Hughes the whole way? The intersection with Lee St isn't listed, unfortunately...the next intersection listed north of Hughes is Conway.