Rare Candy Issue

I am working my through a custom Pokemon game where I have created 250 entirely new Pokemon and a new region as well. I came across an odd glitch today while using rare candy to level up Pokemon. As I level up a Pokemon it works just fine until I reach the level that the Pokemon evolves into it's next form. The result is that it doesn't seem to reach the next level but actually reduces it to the previous level.

For example;
Charmander evolves into Charmeleon at level 16. If Charmander is at level 15 and I use a Rare Candy to level up to 16 and evolve, the result will be that Chamander evolves into Charmeleon. The issue is that Charmeleon's level will be 14.

It's almost as though Pokemon Essentials will register that Chamander is at 15 and evolve but it will trip up and instead of adding 1 level it will reduce it by 1 at level 15.

Any ideas on this one?

Did you do some edits?

It might be an issue with the experience growth rate.
Check to see if their growth rates are the same (medium slow).
If they are not, It will require more or less exp to be certain levels, ending up with lower level evolve pokémon than the pre-evolution.

I have edited:
pokemon - completely created from scratch
trainer - just new trainer entries
trainertypes - new trainer types
items - added new items
moves - added new attacks
encounters - new wild pokemon arrays

I changed the HM move eligibility so that you can use all of them after the first badge. All my edits really don't have anything to do with rare candy.

Yes, but it might not be the rare candy itself that's the issue. Are you absolutely certain that the growth rates for the Fakemon are the same as the growth rates for the pre-evolutions?

This is in fact the case, a basic form Pokemon does not have the same growth rate as it's post-evolutionary form. I basically used Excel and some nifty equations to help me populate the pokemon data file and took it for granted that the growth rates slowed down as they evolved. It seems that this is the issue and that an entire family of Pokemon need to have the same growth rates.