SatoshiLabs shipped their 'open source' Trezor product without sharing its bootloader source code.
When asked about this via their support email and bitcointalk.org forums, SL said they were not going to release the bootloader source code because this would open up the opportunity for clones to enter the market.
This is true -- but then you cannot market your device as 'open source' if you aren't going to release the source openly.
SL did eventually release the bootloader source code for the 1.2.5 bootloader after I shamed them on Reddit.
The initial batch of metal Trezors shipped with bootloader 1.2.0, and SatoshiLabs has not released the associated source code.
VIDEO CLARIFICATION: I have not been able to reproduce the 1.2.0 bootloader from source because the code for the 1.2.0 version has not been posted. (as far as I can tell)