Right now, the default comment summary gets highlighted only when the "Advanced" option is opened for the first time since loading/switching to any Reply mode (Visual/Source).
It does not get highlighted in the following scenarios:
Scenario 1:
1. Open the Reply tool.
2. Click on "Advanced" link.
3. Close the "Advanced" option.
4. Draft a comment.
5. Open the "Advanced" option again.
Scenario 2:
1. Open the Reply tool.
2. Click on "Advanced" link.
3. Close the "Advanced" option.
4. Open the "Advanced" option again.
5. Now switch the Reply mode.
6. Close the "Advanced" option.
7. Open the "Advanced" option again.
Scenario 3: (which might not be an issue if T263061 gets fixed)
1. Open the Reply tool.
2. Open the Advanced option.
3. Close the Reply tool.
4. Open the Reply tool again.
Observe that, the Advanced option is still open but the comment summary is not highlighted.
Browser: Chrome
Wiki: English
Environment: Beta
Page: https://en.wikipedia.beta.wmflabs.org/wiki/User_talk:RYasmeen_(WMF)/sandbox