I'm only getting charged the base 7 mana for a level 15 cleric with 35 cleric spells. Other clerics of mine seem to be paying the right amount when I checked, but although I was being charged extra when I first had 307, I don't think its been other than the base cost of 7 mana for a week or two.

I've stopped and recast numerous times including specifically to check I am getting more than the base benefit when being charged the base cost.

RATHBONER

Still cost 7 mana at level 28 and 49 spells, but started charging extra again at level 29 (jumped to 18 mana)

This should now be resolved (e.g. level 28 with 28-49 spells would cost 17 mana). Thanks for reporting the issue.

GameMaster Estild