The Conditional Formatting dialog includes a button with tooltip "Enabled"
It seems to toggle the status of the conditional formatting based on its effect on the Preview example:
The problem is that this button refers to the enabled/disabled state of the control, not the formatting.
The issue is that the preview behavior seems to imply it enables or disables the formatting. This is because it does not take into account the locked/unlocked status of the control. If the control is locked, then the preview is incorrect - the formatting WILL be applied and will not look like the preview.
As far as I can find, the Access documentation on MS's website provides only a very cursory description of conditional formatting, and does not describe the rule editing dialog (where the "Enable" button is) at all.
This situation really needs to be corrected:
Modify the dialog preview to take into account the locked status and display the actual formatting that will be applied
Provide better feedback on the current state of the "Enable" button
Update the documentation to describe the rule editing dialog