A lot of the synergy has to do with the exact wording of the abilities. In the case of the summoning, there is a difference between the ability that triggers on casting and one that triggers on summoning. The casting triggers when you begin to cast the spell, this can be interrupted by damage or counter-spells, thus negating the actual summoning. The summoning triggers when the creature actually appears on your next turn (or on the current turn if things such as quicken spell are used).
Lemme give you a wildly different example. Imagine that you have four abilities (I'm just making them up, I'm sure there's abilities a little like this somewhere):
1. Make Spells Firey. This allows you to convert any spell which does elemental damage to fire damage.
2. Bonus Cold Damage. This allows you to add 1d8 damage to any spell which does cold damage.
3. Bonus Fire Damage. This allows you to add 1d6 damage to any spell which does fire damage.
4. Generic Cold Spell. This does 1d3 cold damage.
You cast the spell, and convert it to fire damage. Do you get:
1. 1d3 fire damage from the spell, +1d6 fire because it is fire damage.
2. 1d3 damage from the spell, +1d8 cold damage because it is cold damage, then the 1d3+1d8 are converted to fire.
3. 1d3 damage from the spell, +1d8 cold damage, then the 1d3+1d8 are converted to fire, then you add 1d6 because it's fire damage.
In this case it makes a difference when the elemental damage is changed. If it's changed at the point when you cast the spell, it's a fire spell and not a cold spell from the start so #1 would apply.