What version are you running?
3.0 alpha 0 (dev) at https://reviews.reviewboard.org
What's the URL of the page containing the problem?
Observed at https://reviews.reviewboard.org/r/8151
What steps will reproduce the problem?

Enter a very lengthy reply.  In my case it consumed more than one full screen.  I don't know to what degree that matters.
Ticking 'Enable Markdown' takes me way up to what seems to correspond with the original reply.
Next, disabling markdown takes me up a few lines.
Finally, clicking OK takes me way up again with a server error message that quickly disappears.


What is the expected output? What do you see instead?
Don't expect all the scrolling, nor the server error message.
What operating system are you using? What browser?
Windows 7, Firefox 46.0.1.  Forgot to try with other browsers.
Please provide any additional information below.
Attached animated GIF should provide further clarity about the issue.