No idea if this is related to the new firmware, but I wanted to let you know about an alarming thing which happened just now.
After updating to the 12u firmware, I removed and re-paired my Twiddler on my iPad, and confirmed that it was working as expected.
Some time later, I removed and re-paired my Twiddler with my MacBook Air. Again, it was working fine. However, when I woke up my iPad again, the bluetooth icon in the upper-right corner of the screen was still solid, and the on-screen keyboard would not show up in text fields.
I figured the iPad still thought it was paired to the Twiddler, so I turned off bluetooth on the iPad... and then my MacBook shut down unexpectedly. o_o'
Again, this may have nothing to do with the Twiddler firmware! However, I wanted to share my experience because the crash report specifically mentioned "A kext releasing a(n) IOBluetoothL2CAPChannel has corrupted the registry."
Full text of the crash report follows, just in case it's useful.
This is the only unusual thing I've noticed so far. Will continue to test!