InstallPanel overall progress bar should be indeterminate if there is only one pack to install.
The issue still happens to us with 4.3.5. Looking at InstallPanel source, the test (noOfPacks == 1) in the constructor is always false, since noOfPacks is initialized to 0, and it changes to the actual value only in startAction method. So setIndeterminate(true) should probably be placed in startAction method.
I added a pull request for my fix: https://github.com/izpack/izpack/pull/16
The change has been applied for 4.3.6.
The corresponding fix for 5.0 is available at: https://github.com/izpack/izpack/pull/17
Fixed applied to 5.0