Glad using NLists sorted things out.
I haven't used the basic List classes for a while but cannot recall this problem when I did. I don't see it using NLists which DU uses quite a lot of
> No, I am *not* sorting the list each time I add an entry. Rather I am asking MUI to insert each entry into the correct place, so that it stays sorted
I should have worded that better, I assume MUI must run a sort routine to add the entry in the correct place, which for many entries added individually will slow things down. That however seemed not to be the case for you as adding to the bottom of the lists did not help you either. It looks as if the built in Lists may have a bug ??