I have the same problem and I have IE8. It seems that when I type more text than the standard size of the reply box it starts jumping. I have to end up typing my message in word or something and then copy and paste it back in because it makes typing a reply nearly impossible.
I'm using IE8 in this post. You have to enable compatbility view and add orthodoxchristianity.net to the compatbility view dialog box.
Step 1: From IE8
, Click on Tools menu. Select Compatibility View Settings.
Step 2: Type orthodoxchristianity.net in the "Add this website" text box. Click on the Add button.
Step 3: Click on the Close button.
Step 4: Click on Tools menu. Select Compatibility View. Make sure check box appears to the left of Compatibility View.
Step 5: Add all the text you want. Size of text box doesn't change.