We cannot successfully set characterAttribute.underline to false in some textRanges.

(MacOS 15.0 Adobe Illustrator 28.7.1)

Steps to reproduce:
1. New document
2. Make a text frame with contents "ab"
3. Set the "b" to a different fontStyle, eg. "italic"
4. Run the below script, and check the console output.

Expected Result: all tests PASSED, meaning that the underline can be set to true and then to false successfully.

Actual result, test B on the "b" fails.

Script:
```
(function () {

var doc = app.activeDocument,
    tf = doc.textFrames[0];

var results = ['Results:'];

tf.textRanges[0].characterAttributes.underline = true
results.push('textRanges[0] test A: ' + (true === tf.textRanges[0].characterAttributes.underline ? 'PASSED' : 'FAILED'));

tf.textRanges[0].characterAttributes.underline = false;
results.push('textRanges[0] test B: ' + (false === tf.textRanges[0].characterAttributes.underline ? 'PASSED' : 'FAILED'));

tf.textRanges[1].characterAttributes.underline = true;
results.push('textRanges[1] test A: ' + (true === tf.textRanges[1].characterAttributes.underline ? 'PASSED' : 'FAILED'));

tf.textRanges[1].characterAttributes.underline = false;
results.push('textRanges[1] test B: ' + (false === tf.textRanges[1].characterAttributes.underline ? 'PASSED' : 'FAILED'));

alert(results.join('\n'));

})();
```

See this community forum post.

Update: User sttk3 discovered that the bug is actually that Illustrator ignores an attempt to set a characterAtrribute property if the value is the same as the applied character style's value for the same attribute.