Well, it seems to be that the Hitachi HD44780 LCD-controller is the mother of all LCD-controllers, so the KS0070B is a compatible version. You can find more information on
http://en.wikipedia.org/wiki/HD44780_Character_LCD and even download the datasheet there.
On page 9 of the HD44780 datasheet you find the same information as I stated before:
Busy Flag (BF)
When the busy flag is 1, the HD44780U is in the internal operation mode, and the next instruction will not
be accepted. When RS = 0 and R/W = 1 (Table 1), the busy flag is output to DB7. The next instruction
must be written after ensuring that the busy flag is 0.
I have searched the MikroElectronica assembly-code several times, but still cannot find this BF-checking, so I think they just assume that the LCD-controller is ready, but with the high clockspeeds it is rather uncertain.
I also found out that switching off the onboard portleds causes less errors on the LCD, so this could indicate a better rise-and-fall of the signal-bit-slope.
The solution of SNG is nice, but when someone wants to use a PIC18F2550 is does not work. This PIC is a 28-pin version of the PIC18F4550 and has no PORTD.
So it is not a perfect solution for our problem, the LCD should have to work on PORTC as well.
But I want to use the PIC18F2550 with a USB at full speed so ...
I still think that MikroElectronica has to come in to help us out ...