Virtualmin stores most of its configuration data in lower-case and expects existing data to also be in lower-case. However, configuration data is not required to be in lower-case by these applications, so Virtualmin often ignores this existing manually-configured data that is in mixed or upper-case.
Examples include the sendmail virtusertable, local-host-names, and bind zone files. In these cases, if data already exists or is entered manually in mixed-case, Virtualmin ignores it, since it doesn't exactly match the lower-case definition of the domain names that Virtualmin expects.
An acceptable resolution would be for Virutalmin to continue storing its data in lower-case as it does now, however it should be able to read in mixed or upper-case data when parsing these configuration files and accept it as though it were in lower-case already (without changing it).
P. S. -- This has been a pet-peeve of mine for a long time (pretty much since 1.0), although I don't think I've mentioned it before. But now that I am a paying customer and Virtualmin is getting more attention to quality, I figured it's time report it.... :-)
P. P. S. -- In reality, this is probably a Webmin bug, but it primarily affects the use of Virtualmin, so I am reporting it here.