You never drained the longTimer channel, so when you say "We agree that longTimer has fired, right?"; that's not quite true. After you call Reset(), you're still getting the value from the first firing, because that's the first time you read from the channel at all.
The docs are quite clear on this behavior and say "Timer will send the current time on its channel after at least duration d." -- key words being at least and says nothing about when you choose to read from the channel.
The docs are quite clear on this behavior and say "Timer will send the current time on its channel after at least duration d." -- key words being at least and says nothing about when you choose to read from the channel.