In webmin, under usermin->configure module -> SpamAssassin, what exactly does this do?
"When searching spam, check"
Well, if there's an option in Virtualmin that's not documented, and also not immediately obvious what it does, that's probably a bug :-)
I'm not entirely certain what that option does either...
There's a few things like that lingering -- my recommendation would be to file a bug report using the Support link above.