No problem. :)
I'm glad fix it.

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>I had, and I've reinstated this, put a .refresh() to the grid after the dynamic sets.
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>Now here's where I could just say, "Thanks, guys - it's sorted", and sneak off sheepishly, for I've discovered the problem, but I'll be a man and come clean: I was relying on the wrong table. It should have been csrZVARXACT.FIELDVAL and not CENZNFLD.AP_FACTOR.
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>"csrZVARXACT", as the name suggests, is a transaction table for CENZNFLD. Before I created the xaction table I originally had CENZNFLD as its source, and named it thereafter.
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>Anyway, the whole form is complicated, it's hot and sweaty here. Thanks for your attention and sorry to waste your time (but it worked like the old show-someone-watching-over-your-shoulder solution to debugging <bg>)