If engaging the effect in parallel was working (and not sounding too loud relative to bypassed) you weren't encountering what GlennO described.Exactly. This is why I got the level drop. And now thanks to @Bakerman I got a way to implement my intended use in this case. As far as I can tell, this issue is now logical, and I can rest my case. Hehe
But that's something that could happen, and dealing with it (while maintaining effect trails upon bypass) would require extra steps. A "Mute FX In 2" bypass mode that removes the influence of block level & mix controls on dry level when bypassed might work sometimes. A gradual ramp up of dry level when bypassing and (faster) ramp down when engaging might sound better than immediate changes, since the wet signal is still at full volume just after bypassing, and not generating any output immediately after engaging.