Cancer Warning on American Apparel Neon Nail Polish

Yesterday I went into an American Apparel Store to have a look at their neon nail polishes.

I was looking for the yellow one to do a similar look like PShiiit.com did it (see pic below).

Beside that the yellow one was sold out, I was shocked to see the warning on the package:

WARNING
THIS PRODUCT MAY CONTAIN A CHEMICAL KNOWN TO THE STATE OF CALIFORNIA TO CAUSE CANCER, OR BIRTH DEFECTS OR OTHER REPRODUCTIVE HARM

Can someone please explain me this? Why would AA sell stuff that makes cancer? And why is this only in California known?

And which chemical is this?
And why they don't tell about the risk on their homepage? There it only says:
All sales of this item are final. No returns or exchanges.
These unique shades of of high-quality neon color are quick drying and long lasting. Manufactured in the USA. Cruelty free, DBP and toluene free.

They say it's DBP (Dibuthyl Phtalate) and toluene free. Those ingredients are known to cause cancer and might make infertile. That's why the EU banned them from toys and cosmetic products. But if they are not in the nail polish, why they put the warning on the package? This feels like buying cigarettes...

I will write AA and ask them what this is all about... I'll keep you posted.