Unable to provide the record of this transaction since the Presto site right now is down due to the latest steroid injections to get the joints moving better, but can provide a quip from email communication with GO:
[...]
On your return from Eglinton GO, you tap on and closed your trip with a tap when you arrived at Union Station. As per the attached transaction history, there is no recorded tap on at Union Station for your trip to Bloor station. As a result, when you tapped at Bloor, you opened a new trip and was charged $5.30 with a pending charge of $11.90. This is the charge you see recorded on your transaction history when you used GO again on Sept 13th.
Therefore, you were charged = 5.30-2.62+5.30+11.90=19.88. If you had successfully tapped on at Union for your trip to Bloor, your complete charges will equal $2.68. You should have therefore received a credit for $17.20.
[...]
At this point GO and UP Express don’t have co-fares. To receive a transfer credit with GO Transit, I recommend you tap on and off the GO readers for your UP Express trip(s) between Union and Bloor.
[...]
OK, without having the Presto record available to show as proof at this time here, I can assure you that I have *never* used a UP card reader, and never will! I'm meticulous in using the GO readers.
The quote from above is a continuing discussion on a bug in their system. And that bug is in the GO reader as you enter the UP Union Station section. It refused to read my card, after squawking and showing green as well as yellow at the same time on that tap-on.
I had concerns, tried to tap again, nothing happened.
But here's my ace in hand! On-board attendant checked my card for a transaction. It *had* tapped on! And that record is on the Presto website. (As a "fare-check $00.00") It looks like I've caught them red-handed on this one, as this has happened a number of times, so much that first service agent who handled this stated so, and then stated "Don't tap off the GO train incoming to Union, and then on again at the UP Express platform, so it forces the trip to be recognized as one complete trip to that destination. We've had trouble with this, and we're working on it".
lol...maybe they're busy expunging the records on the Presto site as I type!