We have several SharePoint 2010 solutions which we want to deploy to SharePoint 2013 with Visual Studio 2012 running on Windows Server 2012. Site solutions work. But farm solutions just don't. I get the error (you guessed it): A feature with ID 15/... has already been installed in this farm. Use the force attribute to explicitly re-install the feature.
And it does really work with the force attribute, but why on earth do you have to use the force flag? Something has to be different, and if there is an already installed feature with this ID, then why can Visual Studio not uninstall or deactivate it by itself first? This error never occurred with SharePoint 2010 and VS2012, although features are already installed.
Thanks a lot for your effort.