This is indeed a new feature you're experiencing.
Any VSTi will now be able to respond to a volume command. This wasn't possible in the past, you see.
There are 2 distinctions.
1. Playing a note with a volume command -> Sets the velocity for that note, which was always possible.
2. Playing an empty row with a volume command -> Sets the wet/dry ratio of the recently played plugin, which is new.
Basically you've set the wet/dry ratio of the plugin to 04 meaning that its almost muted. Playing a note with a volume command will not change the wet/dry ratio, but instead change the velocity of that note. In order to set the wet/dry ratio while you have a note, either setup a Zxx macro to do this, and use Z7F as value or attach your plugin to a new channel, and just put a v64 volume in that row without a note playing.
Or optionally, it might also be possible to set the v64 in an earlier pattern where the note already died playing.