I have never programmed an LCD display before, so I don't know what to expect. For instance, is it supposed to wrap from the 1st line to the 3rd, then 2nd, then 4th?
Unfortunately the answer is yes.
This behavoir is due to the fact that the same controller is used for all LCD display configurations. For a complete explanation follow the LCD Addressing link at http://web.alfredstate.edu/weimandn.
I am having a hard time believing it is hardware. Seems unlikely that the manufacturer would never have tested one of them and the fault is soooooo obvious
If 'it' is referring to the duplicate display problem that you are having - this is not due to a design deficiency in the hardware it is more likely a problem in your particular pc board. The manufacturer would have to test every board to catch your problem.
If 'it' is referring to the interlaced rows - I have explained the situation above. This has been 'fixed' by at least one manufacturer that I know of (New Haven Displays), but their controllers are therefore no longer completely HD44780U compatible which is a problem for some Arduino users.
Don