it happens if you click on the wrong save button. im guessing you clicked on arbok and pressed the save list 2 button what happens is when you click on a pokemon in a list it tells the program where to save data if you press the wrong save button it will save the data from the other list to the pokemon you have selected. Notice how arbok is the 24th pokemon on list 1 and zoroark is the 24th pokemon on list 2
in other words if you click on bulbasaur and click on save list 2 then petilil data will overwrite bulbasaurs data