Ukrainian: palatal assimimilation vs. spelling?

[Christian Weisgerber]

In Ukrainian, consonant clusters undergo palatal assimilation:

| Unpalatalized dental consonants /n, t, d, t͡s, d͡z, s, z, r, l/
| become palatalized if they are followed by other palatalized dental
| consonants /nʲ, tʲ, dʲ, t͡sʲ, d͡zʲ, sʲ, zʲ, rʲ, lʲ/.
https://en.wikipedia.org/wiki/Ukrainian_phonology#Consonant_assimilation

If you, say, look at a map of Ukraine, there are many placenames
in -нськ(е). The s is marked as palatalized /sʲ/ and the preceding
n should assimiliate to it and palatalize to /nʲ/, too. Pronunciation
entries in the English Wikipedia also reflect this, e.g. Куп'янськ
[ˈkupjɐnʲsʲk]. Given the assimilation rule, there is no need to
write *-ньсь-.

Now, the map also shows many placenames in -льськ(е), e.g. Старобільськ.
As expected, the l is palatalized to /lʲ/. However, here the
orthography explicitly marks it as such: -льсь- instead of *-лсь-.
What's up with that?

--
Christian "naddy" Weisgerber na...@mips.inka.de