Comment 14 for bug 196453

I'm not sure that's a good idea. As far as I know, the Alpha channel value that you're actually adjusting with the slider is between 0.0 and 1.0. And setting 0.0 to be 1% is just going to mess things up if you're actually trying to use a specific value for some reason.

I think it would be far better if the slider hard-stopped at 0% and you had to release it and drag it down to -1% in order to get the 'hidden object' functionality. That would make absolutely as much sense.