It will add an entry to the list only if its not an exact match for an existing entry. But if you are selecting and finding, then yeah, they'll get added too and push your regex down.
Its not intermittently failing to load your text from a Ctrl+F - its got a hard-coded limit so that if you are over 100 characters then it won't load it into the find box.
That does seem a bit low - and something a bit larger might be a reasonable setting if the use case is to load then edit it down to a simpler regex.
Oh, this isn't the saved searches feature, its just the Find history or the Replace history
