"prefix" doesn't prefix xor names

[tirsen]

type DBConfig struct {
	Password         string         `help:"Password" xor:"password" optional:""`
	PasswordFile     string         `help:"File which content will be used for a password" xor:"password" optional:""`
	PasswordCommand  string         `help:"Command to run to retrieve password" xor:"password" optional:""`
}

type SourceTargetConfig struct {
	Source DBConfig `help:"Database config of source to be copied from" prefix:"source-" embed:""`
	Target DBConfig `help:"Database config of source to be copied from" prefix:"target-" embed:""`
}

I get error:

--source-password --target-password can't be used together