We watched this happen again in New York where OMNY was supposed to be the region-wide fare system, but the Port Authority decided not to use it, all the bus systems decided not to use it, and the MTA's railroads decided not to use it. It is a mild disaster. (Hilariously, the Port Authority runs two rail system, PATH and the JFK Airtrain. The Airtrain does take OMNY.)

Does Caltrain still count entering the BART station at Milbrae as not tapping off? That was always my favorite quirk of the Clipper system.

(For those not familiar... Caltrain is a tap on / tap off "proof of payment" system. You're charged the full fare when you tap on, and refunded what you didn't use when you tap off. BART and Caltrain share a platform at Milbrae. You can get off Caltrain and be right at the gate to get into BART by tapping your Clipper card. Well. This taps you into BART, but doesn't tap you off of Caltrain. To get your refund, you had to know this was a thing and go find a fare validator before tapping on to BART. You also end up being inside Caltrain's proof of payment required area without proof of payment while you walk along the platform from Caltrain's fare validator to BART's entry turnstile. I am probably the only person to ever care about this, but...)