Just found the Variety Of Sound free plugins, they’re the shizznit. Anyway setting up this synthesized “piano/keys” sound with a big chorus/echo from ‘NastyDLA’ VST, I’m running into an annoyance: even when you ‘panic’ Renoise (backspace in my setup), when you press play again the delay feedback loop from before will still stay in existence in the VST’s memory. I’m not sure if this is a thing in Renoise or (probably) in the VST - but now I can only render correctly when I freshly load the song file!
Renoise has absolutely no control over how a VST plugin will flush its buffers (or do anything else) when audio processing is suspended and then resumed (which happens during a ‘panic’), so this definitely seems like something to do with the VST plugin itself.
This suspend/resume behaviour is pretty common among all plugins, and is recognized as the method by which a plugin should clear any audio buffers.
Alright so there’s no such thing as ‘reset’/panic in VST land. Soz close topic 
There is, but it’s entirely up to the plugin developer to implement the correct functionality for their effect/synth/whatever. Each plugin has a suspend() function which is called by the host (ie. Renoise) when the audio stops processing, and a resume() function which is called when the audio starts processing again. As I mentioned before, this suspend/resume sequence happens when you hit ‘panic’ in Renoise, and also when changing your audio preferences (sample rate, for example). This is where it’s considered safe for a plugin to do things like clearing its audio buffers, or other potentially heavy calculations. For delay effects, this is where any trailing delays/feedback should probably be cleared, but again it’s totally up to the plugin dev to decide how this is handled. It could simply be a design choice that NastyDLA does not reset in this case.