An intern gets a devboard with a new mcu to play with. A new generation, but mostly backwards compatible or something like that. Intern gets the board up and running with embedded equivalent of "hello world". They port basic product code - ${thing} does not work. After enough hair are pulled, I give them some guidance - ${thing} does not work. Okay, I instruct intern to take mcu vendor libraries/examples and get ${thing} running in isolation. Intern fails.
Okay, we are missing something huge that should be obvious. We start pair programming and strip the code down layer by layer. Eventually we are at a stage where we are accessing hand-coded memory addresses directly. ${thing} does not work. Okay, set up a peripheral and read state register back. Assertion fails. Okay, set up peripheral, nop some time for values to settle, read state register back. Assertion fails. Check generated assembly - nopsled is there.
We look at manual, the bit switching peripheral into the state we care about is not set. However we poke the mcu, whatever we write to control register, the bit is just not set and the peripheral never switches into the mode we need. We get a new devboard (or resolder mcu on the old one, don't remember) and it works first try.
"New device - must be new behavior" thinking with lack of easy access to the new hardware led us down a rabbit hole. Yes, nothing too fancy. However, I shudder thinking what if reading the state register gave back the value written?