Yes, that is what I now believe. Apparently what happens is that the switch diaphragm leaks just a microscopic amount of brake fluid (perhaps only under very vigorous braking), which then coats and eventually fouls the contact mounted on the nominally dry side of the diaphragm. Why that isn't a problem with conventional fluid, I can't say.
Of course, I could be wrong, it's just a SWAG. And many people (like Geo) seem to have no problem, so I feel one could reasonably blame it on poor quality switches. But the first switch I had fail had been working fine for many years with DOT 3/4, and failed within a year (IIRC) of switching to DOT 5. There was still no noticeable weeping from the switch when I removed it, but like the mechanical switch, the inside of the cavity had that "wet" look that I associate with a microscopic layer of silicone. (Like the "wax" they put in the water at the car wash, which is mostly silicone.)
FWIW, I actually had the same thing happen with my pedal-mounted switch. One of the fittings on the MC was weeping a bit, and over time fluid apparently migrated down the pedal and into the switch. When I took the switch apart to investigate, the cavity appeared damp and there was a hard substance on the contacts which I now believe was silicon deposited when the silicone DOT 5 got heated by a poor contact (caused by the DOT 5 in the first place). Fixed the weep, replaced the switch, and it's been working fine for several years now.