I had all five windows tinted in my Z and never had a problem. 
I recently took out the tint from passenger and driver windows. 
Not really sure but i think i have smoked windows , They look tinted after i took the film off, I also cleaned them. 
  
Here is something i think is funny, I drive a ford festiva. 
I took it to the tint shop to tint all five windows. 
Three hours later i was on the right side of 101 . 
I got tickets for tinted passenger and driver windows and the reason he stop me was cause my sticker(month) was faded from the sun, I also had a cracked windshield. 
All i paid was $80 for the tint, Still have my tint on though. 
It's been  over a year without a problem.