I have found the problem and I believe it is a dangerous bug. If the original form I am using is not subclassed - its parent is the generic form- then this problem does not occur. However, if the form I am using has a parent form that has optimistic row buffering set as the default then the only way I can find to keep data from being optimistically row buffered is to set each table in the data environment to have no buffering. If it is set to use the form default it is apparently picking up the default from the parent class , not the present instance of the form. This behavior seems to hold true in the VFP 9 beta also. I hope someone can confirm this and that this behavior will either be documented by Microsoft or altered to something more reasonable. Let me recap :

Form A is a subclass of a generic data entry form.
The generic data entry form is set to Optimistic table buffering
Form A is set to Buffer Mode NONE
Tables in the data environment of Form A are set Buffermodeoverride ='Use Form Setting (default)'
Tables in the dataenvironment are actually in optimistic table buffering mode rather than the expected no buffering mode.