If their library (the one you linked to) matches the hardware you have then in order to use fm's library you will have specify
all the bits for the i2c pins because they are different from the default pin mappings.
(The nibbles are flipped).
So when using fm's library you will need this constructor:
LiquidCrystal_I2C lcd(0x38, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
This should set up the proper pin mappings and the pin mapping and polarity for backlight control.
If you want to use the examples, you will need to modify the constructor.