LCD 16*02 I2C shield only shows first character printed
That's definitely a bug appeared in 1.6.6.
For reference, see
https://blog.arduino.cc/2015/11/03/arduino-ide-1-6-6-released-and-available-for-download/#comment-278766
https://forum.arduino.cc/index.php?topic=359652.0
http://forum.arduino.cc/index.php?topic=357312.msg2476987#msg2476987

Last link seems to provide a solution, by a updated version of LCD I2C lib : https://github.com/marcoschwartz/LiquidCrystal_I2C (not yet tried).

The 1.6.6 is a bit messy according some people, but the I2C lib too ;). So the question is : where should it be fixed ?