Custom brush issue

I've been creating some custom brushes, creating and saving them as a Brush Preset. However, their settings seem to be copied to all brushes, no matter what those might be. If I switch off the settings of the custom brush, but then select it again from the Brush panel, it does not revert to it's previous form and seems to be completely erased. That is, it just follows whatever settings are now in the Brush Preset Panel. This happens both by selecting the brush in the Brush Panel and the Brush Settings panel. It seems that a few hours of work creating these new brushes has now been lost.