When you apply power to pins 1 + 2, polarization voltage to pin 3 on a
4xN LCD, the first and third lines comes up in black characters since it
is "power up preset" to one line mode, so the first line is on (remember
that the first line is broke in two and it extends as the "third"
line).  If your PIC can't change that, it means that your device is
unable to reprogram the unit to 2 lines.  If you don't have an
osciloscope to debug it, just insert delays of 1 minute or more between
data sent to the LCD, so you could measure the state of the lines using
a simple voltmeter.  Just measure all the 14 lines after each change,
make a map and compare to what it should be.

Wagner Lipnharski