Bruji

That would save a bit of time...

Preferences -> Autofill (tab) -> Genre (popup), will list all the genres ever entered. The "rebuild" button will recreate the list from what is in the database, after removing some genres.

It would be nice if we had the option to keep existing genre's that are already in the list rather than having them removed when its rebuilt.

Welcome to the forum. The rebuild button, is sort of a clean button that shows you only what is in your database; if you have something in the list but nothing in the database is marked with that genre then it gets removed. It quite useful to find unusual genres that you want to clean up. But thank you for the suggestion about keeping unused ones around, although unlikely to make it through as it would defeat much of the gain achieved by the rebuild.

So, if you only have two genre's entered they will show up in the pick list without a rebuild?

Yes. The list displays everything ever entered that the program has learned. The rebuild will remove any genres that no longer exist. For example you add a book with "Murder Mystery Fiction", but then decide it's better cataloged as "Crime". The "Murder Mystery Fiction" will still appear in the list, but would not appear after a rebuild as no book carries that genre anymore.

Yes, I did rebuild myself out of all genres except for "manga". Then, I had a mental block of what would be appropriate defaults after staring at that forlorn single entry. I since decided that manga is better off as a tag than a genre. I vote for an additive restore defaults anywhere 'rebuild <x>' exists within a far flung future release.