Installer does not allow to install into existing installation folder

Starting an installer to install a missing component into an existing installation folder is rejected. See image with error message. In version 1.3 one could go further and continue to install into an existing program folder.
Background: We have an installer that has two components, say "Main_program" und subcomponent "Optional_library". In the first run a user installs only the main program and in a second step he wants to install the missing component using the same installer. This does not work anymore in version 1.5. With version 1.3 the user could run the installer again to install the missing component. This is an important bug for us, so we can not use version 1.5.