GetXxx() becomes case-sensitive if called on viper.Sub()?

[ignstv]

For example, I have a YAML configuration file like this:

Server:
   Host: "localhost:8080"

If I read this setting with this:

host := viper.GetString("Server.Host")

host contains the intended value, but if I read it with this code:

host := viper.Sub("Server").GetString("Host")

host is empty.
Further debugging reveals that with Sub(), viper seems to store the configuration with exact case ("Host"), but on GetString(), the query key is lowercased and the comparison "Host" == "host" fails.
According to the doc, I thought viper was case-insensitive, so maybe this is a bug?