When the firmware is newer than 52.84, I found that the phone can't handle multiple frequencies (harmony tone) the tones consist of 2 or more notes (Yealink supports up to 8 notes).
Example:
!220/333,!262/333,!440/333,!349/333,!294/333,!349/333,!587/667,523+466/20000
In this case, 523+466Hz, only 523Hz will be heard. Only the first note supports multiple frequencies.
I just upgraded the newest firmware as of today. And the release note didn't mention this problem. Therefore, as expected, the problem is still there.
Example:
!220/333,!262/333,!440/333,!349/333,!294/333,!349/333,!587/667,523+466/20000
In this case, 523+466Hz, only 523Hz will be heard. Only the first note supports multiple frequencies.
I just upgraded the newest firmware as of today. And the release note didn't mention this problem. Therefore, as expected, the problem is still there.