I have observed this several times. Sometimes, Ice Burst does no damage. It's just a very fancy VfX. I can't find a pattern to it. It can happen when targeting the floor or targeting a NPC directly. The spell bugs infrequently, and the next casting directly after the bugged one might work fine.
Maybe your opponents rolled all the reflex saves and had evasion?
No, there's no save rolled. Also, I've seen this against opponents that I know don't have evasion. Done it on large groups as well, including allies who I -know- didn't have evasion. Those who've traveled with my PC extensively can vouch for this happening, I'm sure.
I've seen this happen many times in the company of Cap's character. I may be mistaken, but I've believe I've even seen enemies get aggro'ed by the spell in spite of taking no damage.
I can vouch for this. Doesn't happen often but it can be pretty disheartening when the swarm of enemies all stay at uninjured after an avalanche falling on them!
I hate to team up with someone affiliated with the hated and rightfully maligned element of ice, but I just started a bug thread that I'm having with another custom EFU AoE spell, Blast of Flame -> [thread]90324[/thread]
These are noted, and will hopefully get fixed when there is time to sort it out, but there is no ETA.
Should probably be fixed after next reset.
Love dat ETA
Thanks Paha!