This question involves Trezor One, Trezor Suite, and Metamask Firefox extension on M1 Mac. Latest and greatest firmware/software versions for everything.
I’m a long time user and have a good understanding of Trezor operation (I thought!), but I was confused by something recently. I have two hidden wallets with different passphrases. One of these wallets is connected to Metamask via TrezorConnect(?). I recently used this wallet and was prompted for its passphrase, made my transaction, all normal stuff. Then I went into Suite and made a transaction with my second wallet (and was prompted for its passphrase of course). Then (this is the confusing part) I went back to the first (metamask connected) wallet to make another transaction and I was not asked to re-enter its passphrase (and the transaction completed normally).
So the last passphrase that I approved via button presses on my Trezor was for Wallet 2, but my Wallet 1 (metamask connected) transaction worked fine. This kinda broke my brain because I thought only one wallet could be loaded on my Trezor at a time and I had to manually enter/approve passphrases to switch between them. Is this not the case? Is there some kind of “active session” or passphrase caching going on?
Yes, this is expected behavior. Since version 1.9.0, Trezor can hold 10 concurrent sessions, so you can have up to 10 “active” passphrases, and don’t need to re-enter the passphrase until the device is disconnected.