maintenancetool.exe and other 'meta' files ignored in disk space usage estimate

For an obvious example, create an installer with no actual data. Run the installer. It will say, "Installation will use 0 bytes of disk space". Click install. Check the size of the installation directory: In my case, it is 25.6MB.

This may seem like an insignificant quantity compared to a huge payload like Qt, but most applications are much smaller. It could cause confusion (and possibly installation failures if IFW is using the same figure to decide whether installation can proceed) where disk space is limited.