Enchanted Shrines

[weakwarrior]

I've just checked that. My rouge character level 17 had got only 1 spell, and that was healing spell level 1 and after taking enchanted shrine (normal one, not random) on dungeon level 3 spell remained on level 1.
And yesterday I had in IM, me as warrior with only 1 spell - healing on spell level 1 and I took goat shrine on dungeon level 6 and it was enchanted - spell remained on level 1.
So probably there is some additional rule that if you have only 1 spell ... smth.
For now we know that first all spells got +1 and then one of spells got -2 (it explains why 15 spell levels ends on level 13, when chosen to decrease). But it is not enough, because if character have 1 spell only, let say on spell level 2, he shall landed on spell level 1. And for spell level 1 on spell level 0. I don't know how exactly is that rule goes for it. Maybe just like if only 1 spell is known do nothing?

That was what I was thinking, although there is no mention in Jarulf's guide that I could find. Can someone who can read code add input?