How much of an issue is (unwanted) plugin introduced noise/distortion in the real world?

I've noticed that a synth plugin I bought has unwanted components when playing a constant sine wave (no VA stuff or effects, just what should be a pure, clean sine), even on highest quality - they're about -70dB peak quieter than the filtered signal and consist of mostly harmonic components (which probably is why I didn't notice until popping it into an analyzer).

Would this be an actual issue? Is it worth filing a bug report (I understand devs can be busy and don't wish to waste their time)?

How common is this problem?

I've heard that plugins from a big name company have an analog button that introduces electrical noise, but that doesn't really count too much because it can be turned off at least...