I know what was that. I was one of the people that reported this bug. In fact, I still have the ticket where I described the bug.
So, in short you could easily snatch a bunch of spells from Dawnport for free. It was a bizarre bug that was most likely left this way since the introduction of Dawnport. The trick was that only not so common spells to pick in Dawnport were chosen. For example, you always would lose light healing or cure poison once leaving Mainland. But rune spells would not be taken away from you!
I discovered it by accident with a character that I levelled up until level 20 and bought all rune spells possible in Dawnport. After that, I burned many mana potions there, just to reach Magic Level 20 (the maximun allowed in Dawnport). When I reached Mainland, I got EVERY rune spell available for druids until level 20, which is quite a big deal.
Some runes that you can get from spell runes of Dawnport:
Information retrieved from: https://www.tibiawiki.com.br/wiki/Hamish
Text above retrieved from: https://www.tibiaqa.com/1584/which-rune-is-the-best-choice-to-make-want-to-train-magic-level-on-dawnport?show=1584#q1584
Needless to say, I reported this bug once I discovered and I never revealed about the existence of such problem. That's what every player should do when facing such occurrences. Curiously, Cipsoft didn't remove the free spells from the noob character that I mentioned to them in the support ticket. I wonder how many people get away with this bug and didn't report it. I suspect that you could get Cast Arrow and Destroy Field spell with a paladin as well, but I am not sure.