I've had this problem before, and it randomly popped up again today.
This time restarting Ai fixed the issue the first time. I just don't know if this was human-error/setting on my end, or a minor bug to report.
So I create a CMYK Ai doc. Create some black text and/or shapes. Then decide to change color to rich black by manually entering CMYK values (in this case, 60, 40, 40, 90), select ok. However, the colors revert back to original percentages (75, 68, 67, 90).
Anyone else have this problem? In past versions, it's happened once or twice, and restarting Ai didn't solve the first time.