I do not know which version of RoundCube is within the package.
I use RoundCube for quiet some time now as a second webmail client for my clients, because it is still in Beta.
I've setup RoundCube according my own howto, which you can find here:
, using the latest Roundcube version.
Soon i will change the howto, so that it is also possible to login with email@example.com
With my setup and at the moment it is only possible to login with the lohin name as defined within ISPConfig.
Personally, I prefer this method, because i can maintain it myself with full control over the version and at it will work on port 80.