To replicate this issue:
1) create a forum
2) create a topic for that forum
- when creating the topic, make sure you make the description about 15 lines long so you have to scroll a bit)
save and post the topic
3) As instructor/student, go into that topic, choose "Read Full Description" link.
The full description will drop down, then automatically go back up. The "Read Full Description" now says "Hide Full Description" but it is no longer showing.