Flame arrow and isaacs missile storm (lesser and greater), both have same effect on a mantle. After like 3 or 4 spells a mantle will falter depending on how strong a mantle you've cast. This bug is a very old one and has been fixed very often, tho ppl usually forget taking care of flame arrow since it's not used very often (reflex save).
If we use isaacs lesser missile storm it hits 10 times. In this case it hasn't been made as 1 spells that does 60 dmg, it's 10 missiles each doing 6 dmg, so it'll eat up the mantle. The spell isn't supposed to do that and I'm guessing mel has taken care of lesser isaacs, but forgotten about flame arrow.
Lightning ball probably has the same effect, but I don't know that for sure.