I've not been able to reproduce the issue. Could you tell me the exact version the issue occurs? Also, which flavour of InstallBuilder are you using? Regular or the QT version?
It happens with regular InstallBuilder 19.11.0 and 20.7.0, on macOS Catalina 10.15.6 on at least two different systems, my dev system and on an installer QA system. We never used the QT version.