Long text fails to expand when "Read More" link is clicked in "Activity" tab of "Activity" heading.

When a long text is entered in description of any task/bug then in Activity tab it gets wrapped up. A "Read More" link is available in new line below the activity text and above the time-stamp. On clicking the "Read More" link, the wrapped text should expand so that the whole text should be readable. But this functionality seems to be broken (as the text fails to expand).
Steps To Reproduce:
1. Click on "Activity" tab (under Activity heading).
2. Notice that the text "Description" field is wrapped and "Read More" link is also available.
3. Click on "Read More" Link
4. Observe that the wrapped text fails to expend.

Note: As the whole text can be see above (in description field) or by simply scrolling up the page (as per JRA-29750 this is intended feature). So "Read More" link should not be present if it is not used to expend the text.

Please see the attached screen shot for more clarification.