Pokemon's names only change if they are evolved under 3 different conditions. That would be:
1. Pokemon with capitalized names from previous generations
2. Pokemon with a foreign name
3. hacked Pokemon with a hacked nickname that didn't set off the nickname flag.
If the Pokemon has a legit nickname, it will not change when it is evolved; and chances are; if it's name changes and it isn't a foreign one, it is hacked. Also, there are no Pokemon games in which the nickname changes if it evolves if I recall correctly.