Pokemon that spawn in underground water can spawn in levels far higher than the "maxLevel" argument in their underground water spawn configs. Other spawn locations seem unaffected.

To reproduce:
1- Obtain a level 100 Pokemon.
2- Go to underground water pools. Spectator mode is the easiest way.
3- Observe as water Pokemon spawn with unreasonably high levels. For reference, the two most common underground water spawns Magikarp and Barboach have their maximum levels set in the configs to 20 and 40 respectively.

There's a config option on by default in that the lower underground you are, the higher level the pokes will spawn as. Lvl 100 Lairons has been a pretty commonly sighted sign of this.