I've found that some lcd's like to have pull up resistors on the control lines - say 4k7 especially if you run a bit of flat cable. My only explanation is that the pull up of the 8051/2 is not enough - for cpu's like PIC and AVR that have active hi drive the issue doesn't occur. Also what port pins you use also has an effect as port0 (I think) doesn't have pullups.