This weekend I went on a building tear and boxed up several boards I had sitting around. I was using the 3PDT Bypass board I gave away last month for all the builds. Two of the builds worked fine. One build, though, caused a major headache. The dry and effect signal were bleeding off in both switch states. I was able to eliminate problems with the 3pdt switch and errors in the bypass board manufacturing. What was different in that last build was that I used metal jacks instead of the isolated Lumberg ones I've been using for the last couple of years.
What's different on the bypass board than the normal wiring I do is that the effect output is also grounded on bypass like the effect input. This is usually a pain when doing the bypass by wiring but easy enough when using a PCB. However, it seems as though grounding the effect output can cause problems when using metal jacks. I'm not totally sure why and maybe someone smarter than me can figure this out. Best I can tell is that if there is a volume pot attached to the effect output it can either cause some kind of impedance issue or provides an AC path to ground via the pot. It doesn't seem like that would happen but it's the best I got so far.
So, if you are using the bypass board then I suggest using isolated jacks like the Lumberg or Marshall type. Or, if you only have metal jacks simply cut the trace on the bottom of the bypass PCB demarked by the green line in the pic below.
Sorry for the mistake. It's something I've never run into! I'll be doing some more of these to give away in December and I will take out the output grounding part for that run.
I may have spoken too soon on this. I kept having the same problem using different styles of 3PDT boards (not just this one). In the end I discovered the issue came from some super cheap metal jacks I was using. Apparently their poor construction lead to tip/sleeve connection through the enclosure. Once I changed them to quality jacks (Switchcraft, I think) the problem went away.
So, I don't it's necessary to cut that trace shown above. I'm fairly sure it was just those crappy jacks I was using.