It is the law, and if you have a local officer after you it can be a problem. But they still have to prove it and this is pretty hard to do. It is especially a problem along the state border towns between Cali and Arizona, Nevada, and Oregon.
Then comes the State work/resident income tax situation....
Az honors dual Residency. 51% of the year is honored as a legal resident. But Cali does not honor it in return... If they want to get you, 15 days is it...