It appears that MsCatSelect does a good job up to 10 categories on a page. When I edit pages that have more than 10 categories, all except 10 are eliminated. I have pages with up to 60 categories. Yes, I know that may seem silly, but there is a reason for it.
So, it's not tolerable to have an extension that deletes existing categories.
Is this a feature? Or a Bug? Is there a fix? I need to allow pages to have up to 100 categories for my system to be useful. See http://wikidelphia.org/Wikidelphia:About to see what we're doing.