Just to close the thread...

The HD44780 is branded with a "U" , so it may/may not have the bugs that Menno referred to.

The character size cannot be altered from 5x7 +c & 1/16 duty so there are few option there..

I re-wrote the drivers to wait until the busy flag was lowered,or until the max operation time (4,8ms) was reached..
And the displays have worked flawlessly since..

Many thanks to those who replied..