I downloaded the latest version of the teensyduino program and looked at
the analog.c implementation. I see you are using the alternate channel set
by setting the MUXSEL bit:

Can anyone explain me what is the reason for doing so? In my application,
I do not use this bit. I re(re...)read the datasheet, and I do not understand
why you do not use channel set A. I fear I am missing something, as both
your version and mine are working.

Thanks for you help,