Shard affinity?

So I just got Soldier Eddie, and I happened to have a couple yellow shards in my inventory, so went to power him up. In the preview, it showed the two shards taking him from level 1 to level 9, I used them, and the little experience bar charged up to 9, but then suddenly he was reduced to level 6. It basically gave me those levels, then stole them!
On other occasions, I've noticed some characters end up at a higher level than the one in the preview.
I know the shards have affinities, but I figured they worked best on characters of the corresponding class, I.E. yellow shards work best on Gunners, blue shards on Magi, etc. At least, that seems to be how it works with runes: red runes work best on red talismans, etc.
Do the shard affinities follow the character class damage scheme? Or some other scheme? Or does my game have a glitch?

Yes, that´s how it´s working. However, there´s a bug going on that gives you less Exp than you would actually get. I had that, too. Showed me that my character would go to 80, but it only went to 79 and I had to use another shard. Kinda annoying because you have to use up more shards and money to level your character. Rainbow shards in general do give more Exp and are not bound to a class, though.

Happened to me too. Usually it works proper.
I think of it like a cashier giving me the wrong change. At least the till was open and I didn't have to wait an extra 15min in the slow line.