>Thank you, that explains why my work-around worked; as macro substitution would change everything to literals. I had tried assigning the passed parameters to form properties, but I still had the same problem, until I used the mac. sub. in an attempt to confirn the condition the filter was using.

This is an example of when using macro-expansion makes sense; resolving the argument to a literal let the variable scope not affect the re-evaluation of the expression after the original macro-expanded variable had released.