Maybe I'm a bit late to the party :)
I took a used unit a few days ago, just for fun and to try something new - I'm not really a guitar player anymore since many years... but I've been very disappointed noticing this issue... Moreover, the patch changing is not seamless: there's always a small gap of silence between them. What I want to try is changing between patches that has the same delay or chorus settings, only with different "mix" values (or the same amp+cabinet combo) to see what's giving those gaps.