Filtering a Table Using Calculated Fields

Hi,
I'm trying to discover why I am unable to use the OnFilterRecord event
handler to dynamically filter records using calculated fields as filter
criteria.
I've set up a Table with 2 calculated fields, each of which are enumerated
types and the only criteria which work are the zero values - implying that
the fields are not being calculated.
I've tried kludging a specific OnCalcFields event just before the filter,
but it doesn't have any effect - the calculated fields remain at zero.
Any ideas out there??

Cheers!
Robert Priest