Crucially, this only happens next to a note + instrument combination and only if there isn't a regular volume command yet, because the code path for handling default volume is not guarded by format checks. I guess we have to disable this feature for MOD, because it would be strange if the first Data Entry interaction places something in a different column (having to "move" the volume effect to the regular effect column), and then it cannot continue doing anything in the volume column becuase now the "virtual" volume command is no longer shown there.

Fixed in r19968.