I have noticed this for a few days.
When I reply to something in IE10, the post appears in the thread without any LF's (BR) visible. If I immediately edit the post and save (without making changes), the LF's reappear.
Screenshot 1 is what I sent (before I sent it)
Screenshot 2 is what appeared once saved
Screenshot 3 is what it looked like after Edit &amp;amp;gt; Save
p.s. also note the two file upload controls, of which the left hand one doesn't work!