Without seeing your file, I can't be sure, but I think you could easily sort this out by clicking on white space somewhere else on the sheet you've filtered - that clears the filter. Check out this example from the Guardian data blog: http://www.guardian.co.uk/news/datablog/interactive/2011/sep/30/crime-map-us-data
Click a State to do a filter. Then click somehwere not on a state to clear it. I added an annotation "Click here to clear the selection" to assist the user.
Does that help?
Thanks Andy - worked a treat !