There seems to be a length limit on custom lists. After I add a certain number of characters, if I add any more older ones disappear, both in the editor page and when I 'browse' the list. Is this the case? If it is, is there any way to extend the number of words allowed in a custom list? If not, why are some of my words disappearing?

There's an unofficial limit of 100 sections, but no one has come close to that limit. I haven't coded in a warning if people try to make that many sections, though. And the sections don't have any particular limit.

I think I found the bug though, and we're uploading a fix now. You probably noticed how the definitions get fetched after the page exits the loading page, so that you can start editing while you wait for all the more detailed data to arrive. Well there was a bug that, if you tried to process the list while it was still loading those definitions, it would miss the words that it was in the middle of fetching. And it fetches five at a time, so those would be mysteriously skipped.

Sorry for the bug!