The F-Curve Modifiers "mute"-Icon recently got updated from the speaker icon to a checkbox.
The checkbox however now does the opposite of what you might think: It disables the modifier if checked and enables if unchecked. The average user doesn't know this is because the actual property is called 'mute'.
This issue was recently pointed out by Pablo in Blender Today's live stream 038 at 44m25s: https://youtu.be/67NIL5A-07c?t=2665
In this Diff I swapped the checkbox to act as expected and changed the Tooltip. The property itself is still called 'mute'.
This is my first little contribution to blender code. I appreciate any feedback and hope I did everything right.