FabFilter

I have ProQ3 on an audio track that is bussed to my record track. I have a short 1k tone that goes for 1 frame. When I have a LoCut or Bell enabled there is signal in my recorded audio after the frame of tone - the waveform looks like there is a very low reverb tail (I know there isn't but that's what it looks like).
No other plugins in chain and the track goes directly to the record track. I've got the March 2019 version of the plugin. I'm also finding this with ProQ2.
Is there a setting I'm not aware of that is causing this?
I don't see a way to send a screenshot which is too bad cause that would do a much better of explaining this than what I'm doing..

This is the post ring that is the result of the filtering process. Every EQ plugin (or analog filter) will generate this.

Cheers,