So ever since the Brand bug fix, I've had this situation happen quite often. Whenever I would ult someone the ult would hit them and then fizzle out as if they had nobody near them. This however was while they were either inside or next to their minion wave. I thought it was a visual bug but the surrounding minions didn't have any damage taken or my passive on them. A friend of mine reported experiencing the same bug as well.
There are now about 10 and still more threads about brand ultimate bug and STILL see no answer from a riot dev!!!
This bug happend to me in my promos then in normal and I have a video to proove it Brand vs Fizz http://sendvid.com/4vo5niqr
Brand vs Graves http://sendvid.com/nhika2sn
Ps: I dont have any application to registre the video appart my phone
Just happened to me to be jhin. It bounces when there are champs clumped, but when it's a champ and just minions it does not bounce.
It happens to any champ, they don't have to be sheilding. Seems to be repeatable by using the ult when it's just 1 champ surrounded by minions and no other champs. Very game breaking for Brand players, makes you miss kills you would have otherwise gotten. 
it goes through yasuos windwall sometimes too
Please fix......if it wasnt already hard enough playing an immobile mage try doing it pretty much without an ult.
I've experienced this bug numerous times and it's cost me a kill in lane and cost me several team fights. It's even worse when you have two running champs that are ablaze and it jumps all the way back to a minion ignoring the clumped up champions
