Spells: Cantata of Replenishment doesn't override Hymn of Restoration

[Lazortag]

Cantata of replenishment has the same effect as hymn of restoration except that it gives mana as well. When I try to use both at once, Cantata will not take hold if I have hymn up (or rather, if I casted it in the last 12 seconds, even if I click it off - but that's another issue), however Hymn will replace Cantata in the songs window if I cast Hymn after. This makes no sense; stronger spells should override weaker spells.