This picture is the only thing I have currently.
But as you can see on the picture it says "Spell immune" but she was still polymorphed.
A few REDDIT users also tested this (100% reproduction rate): https://www.reddit.com/r/leagueoflegends/comments/5zxgti/lulus_polymorph_interaction_wtih_morganas/
edit: another picture
It seems that game was last patch, but I did find something else interesting https://youtu.be/I66SXm--nHA
Lulu's polymorph failing to cancel my teleport
Just thought I would stop in and give another example,Sion's ultimate says it makes him immune to ALL CC in the description, but somehow I was polymorphed out of my ult. I'll edit this with a video of it as soon as I get the replay clip made and uploaded
Edit: Unfortunately the replay expired this patch, which sucks
TBH, Lulu has several bugs and issues with her Polymorph. For example, I have had people continue to AA or use spells through it, despite being poly'd. Her shield is also really wonky and over sensitive as sometimes you can self cast, it will go on CD, but then give no shield. Sometimes I believe its gone on a minion but other times I honestly don't know what's happened. :/
There was also that One for All Lulu game I played where I was top lane and the two lulu's bot lane killed their laners but I some how got a double kill? XD
tbh just making it into a stun (and keep the particle effects) wouldn't make her too much more powerful. And probably fix all the related bugs.
Lulu's polymorph just ignores CC immune targets these days. Through Sion ult, through Fiora's Riposte (seriously, mulitple times in a single game), and now Morgana's black shield.
It also stops Sion's ult...
