@Bumidek I know whats the problem:
You've got data under the "Met" tab. (example)
1. Only Pokemon originating from Crystal get information stored into in that tab (retained when traded to GS)
2. Additionally, Pokemon traded to Gen I (let's say, to learn TM moves) lose that data.
So it's not a bug. Look, at Gyarados of mine, without the data there, is legal.