Spell Calculation error

[Lawful_g]

Something seems to be wrong with the spell array. All 9th level spell numbers are being reduced by 1. For example, at 20th level wizards should have 4 9th level spells, but HL is showing only 3 slots.... I have tested with cleric and several other spellcasting classes of my own devising (where I varied the number of spells and saw it is always 1 less). It only seems to be 9th level spells that are affected.