I use Webmin 1.530 on Ubuntu 8.04 with Apache 2.2.8. If you go to Webmin/Server/Apache/Global configuration/Misc/Server HTTP Header and set this to "Product only" (german: "Nur Produkt"), Webmin writes a wrong string into the Apache config: Webmin writes "ProductOnly", however "Prod" would be correct. Apache-conf excerpt:
# This directive configures what you return as the Server HTTP response
# Header. The default is 'Full' which sends information about the OS-Type
# and compiled in modules.
# Set to one of: Full | OS | Minor | Minimal | Major | Prod
# where Full conveys the most information, and Prod the least.
After applying configuration to Apache through Webmin, Apache uses sometimes Full and sometimes Prod. I have to make this setting manual, Webmin does not do it correctly.
Hope I could contribute enough details.