VST Plugin get parameter assertion

I’m hosting VST Instrument plugins in my Sequencer’ish App
I recently tried to use XFer Records ‘Serum’ VST plugin and I got an assertion when I clicked some button in the plug for unrecognized parameter index received from the plugin.
It is probably fair to say it’s the VST responsibility to report a change for a valid parameter index that was registered before, but I’d still like to be able to use this standard VST plugin in debug mode.
The assertion occurred in VSTPluginInstance::handleCallback():1621

Is this assertion indicating a more serious problem, or is everything still working OK?

We’re not going to remove it - it’s a valid signal that something could be wrong. You’ll have to modify your copy of JUCE if you don’t want it triggering. You’ll find similar things with plug-ins not handling gestures correctly too.

This is what I did…

I generally agree with you, but in practice it has no influence. The plugin was just informing the host that a button was clicked that has no corresponding parameter registered in the initialization of the VST instrument.
I’ll investigate the VST API requirement whether this is a legal action and settle this down.