Unset "git flow config" value doesn't work

[jrebmann]

I tried to unset my version tag prefix configuration.
On initialization I set the version tag prefix to another value:
git flow init -d -t "v"

Now I'm not able to unset it with following command:
git flow config set versiontagprefix ""

[Konano]

I solved this problem with git flow init -f, to set all config again.