Installer should do some checks when trying to install same version

Currently, it is possible to install same version to the different directories within system. This leads to one problem - under Windows, installer creates only one entry in the "Programs and Features" and overwrites it with the second installation. Also, some programs can't be installed in this way - program may not be able to share files stored in user directory between different application instances.

There are some ways to solve the problem.
1) Always allow to install in different folders. In that case, installer should create different entires under "Programs and Features"
2) Always deny installation in different folders. This requires some check when installer is launched - the best approach is to switch installer to "Maintain mode" (with package manager/updater/uninstaller) if application in already installed.
3) Combined variant, allowing developer to choose behavior via config.

I prefer option 3, however i will be satisfied with option 2.