The game saves the ignore list as a file. The file's name includes the account name you used to log in. The catch is that it uses the exact name you used to log in, rather than your canonical account name, even though the game itself is not case sensitive for the purpose of logging in.

What this means is that if I log into the game using 'Pizzasgood' and ignore some people, then log in the next day using 'pizzasgood', the game won't recognize the previous ignore list. Instead it will create a new list using the lowercased variant, which doesn't include those people I ignored previously.

I've seen this behavior in Linux. It probably doesn't happen in Windows, assuming Windows still uses a case-insensitive FS.

Huh, interesting. Thanks for the report.