I think I found a bug!

I redeemed one of my cold storage addresses and sent 1 output to a "3xxxxx" multisig address and the remainder to my TREZOR. Now the address of the Trezor was obviously not a multisig address. BUT! The trezor now shows it got the coins sent to a multisig address.

This is the address that is now shown in my TREZOR: 35cAcatwpoL5gbKF2Raahuh1Ts62eh3n16  (have no idea where it got it from!)
This is the transaction: https://blockchain.info/tx/257c8f37b48179668a07d1b0a25e864c3c28ea0b7dccdd96d80bd5b16ddb6cc5
The Trezor address is the 4.9999 output.