Thanks Erel, that's what I thought. I'll rewrite my filter code to check for apostrophes.
What do you think - perhaps it would be a good idea to have a filter command that just dealt with variables, as I imagine this is how it is often used? At present, using different syntax for numbers and strings makes it a little more complex - but perhaps that is just my application, which has a one button filter of the selected column by the contents of the selected cell. I need different syntax depending on whether the column holds numbers or strings. Which is not too difficult. But then adding code to look for apostrophes!!!