Lines 39 to 42 of sendmail/aliases-lib.pl remove
comments from the list of aliases. Unfortunately, they
also remove disabled aliases (since those look like
comments). No webmin user can then regain access to
modify/enable/etc any alias that is disabled.
I haven't had time to figure out what the
comment-detecting regex (/^\s*#+\s*(.*)/) should
properly be, so my workaround was to just delete lines
39-42 and modify the subsequent "elsif" to "if".