Tales of Destiny R is a result of timeline changes.
Tales of Destiny and its remake have some noticable differences, from minor things Stahn and Lion no longer using a shield, to major things like Lion dying a hero.
This is because in Tales of Destiny 2, all of the influences to the time line done by Elraine, Fortuna, Barbaratos and Kyle's group changed it to the point that Fortuna's death wasn't enough to completely reset it.
The personality in Swordian Berselius isn't Karell- it's Harold.
Berselius never actually speaks as itself, just Miktran, who was possessing it. Berselius has a gold core. Most of the Swordians have silver cores, and the only other one with a gold core is Atwight, which used a woman's personality. Karell was the one who originally wielded Berselius, but it was made by his eccentric sister, Harold, who regularly does things simply because she thinks they'd be entertaining
. It seems reasonable that she'd put her own personality into her brother's Swordian as a prank.
- She's extremely broken up by Karell's death, suggesting that they had a fairly close relationship, so it also wouldn't be unreasonable for her to put her own personality in his Swordian out of a desire to always be there to help and support him even when she couldn't be there physically.
- According to the English translation of the Tales of Destiny 2 script, this is confirmed by speaking with Karell after he receives his Swordian, but maybe someone who can actually read Japanese should make sure this is true?